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A level Biology > Unit 4.3 - Inheritance > Flashcards

Unit 4.3 - Inheritance Flashcards

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1
Q

Heredity and genetics

A

the study of inheritable characteristics

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2
Q

phenotype

A

appearance/characteristics that are controlled by genes

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3
Q

genotype

A

total alleles possessed by the organism

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4
Q

alleles

A

different versions of the same gene

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5
Q

example of alleles

A

different alleles for different eye colours

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6
Q

what are the two possible types of alleles?

A

dominant and recessive

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7
Q

dominant allele

A

always expressed in the phenotype (represented by a capital letter)

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8
Q

what type of allele is always expressed in the phenotype and which type isn’t?

A

dominant is, recessive isn’t

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9
Q

recessive allele

A

only expressed in the absence of the dominant allele (represented by a lowercase letter)

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10
Q

alleles for the number of fingers gene

A

5, 6 (rare)

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11
Q

alleles for the freckles gene

A

present or absent

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12
Q

alleles for the rhesus blood group gene

A

positive, negative

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13
Q

what is the rhesus blood group gene?

A

gene that codes for a protein in the cell membrane of blood cells

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14
Q

how are some genes different to others expressed in the phenotype? give an example

A

some may be hidden and are part of our biochemical makeup so we have the test for them. for example, rhesus blood group

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15
Q

who was darwin influenced by for many of his ideas for the theory of evolution?

A

gregor mendel

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16
Q

why was it difficult for gregor mendel to come up with his laws?

A

the chromosomes hadn’t been discovered and nobody knew about meiosis etc

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17
Q

what did gregor mendel use to come up with his laws? how?

A

pea plants and he compared their colours and seed shapes to come up with the laws of inheritance

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18
Q

what type of laws did gregor mendel come up with?

A

the laws of inheritance

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19
Q

Mendel’s first law

A

an organisms characteristics are determined by factors which occur in pairs. only one of a pair can be found in a single gamete

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20
Q

Mendel’s second law

A

either member of an allelic pair may combine randomly with either of another pair

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21
Q

gene

A

a length of DNA on a chromosome normally coding for a specific polypeptide

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22
Q

locus

A

a specific position on a chromosome where a gene is located

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23
Q

alleles

A

different forms of the same gene

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24
Q

what is an allele always represented as?

A

a single letter

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25
Q

dominant allele and how its represented

A

will always be expressed in the phenotype when present
represented by a capital letter

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26
Q

recessive allele and how its represented

A

will be “hidden” when a dominant allele is present in the heterozygote. a recessive allele will only be expressed when it is homozygous
represented by a lower case letter

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27
Q

codominant

A

alleles that are equally expressed in a heterozygote (both versions of the gene expressed in the phenotype)

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28
Q

phenotype

A

the characteristic of an organism resulting from both its genotype (inherited) and the effects of the environment (its not just controlled by genes!)

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29
Q

what does a phenotype result from?

A

both an organisms genotype and its environment

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30
Q

genotype

A

the genetic make-up of an organism i.e - its alleles
always a pair of letters

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31
Q

what is a genotype always?

A

a pair of letters

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32
Q

homozygous

A

both alleles for a gene are identical

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33
Q

heterozygous

A

both alleles for a gene are different

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34
Q

F1

A

the first filial generation - the offspring of the parents in a genetic cross

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35
Q

F2

A

the second filial generation - the offspring of an F1 plant that is self-fertilised or a cross between twp members of the F1 generation

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36
Q

autosomes

A

chromosomes which are not sex chromosomes

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37
Q

sex chromsomes

A

chromsoomes which determine the sex of an individual organism (x and y)

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38
Q

what are the 2 types of sex chromosomes?

A

x and y

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39
Q

what are the two types of chromosomes?

A

autosomes
sex chromosomes

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40
Q

give an example and explain a codominant allele

A

snapdragons
by crossing a red flower with a white flower, a pink flower is obtained
therefore, both alleles have been expressed in the phenotype

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41
Q

homologous chromoeomes

A

carry the same genes at the same loci

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42
Q

what’s different between homologous chromosomes

A

there may be different alleles of the same genes

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43
Q

compare the dna from one chromatid to the other within one chromosome

A

the dna in each chromatid is identical

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44
Q

true breeding/pure breeding

A

homozygous for every gene
=offspring with the same phenotype

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45
Q

what happened when mendel crossed a pea plant which was true breeding for tall plants with a pea plant that was true breeding for short plants? what happened then when the F1 generation were crossed?

A

the f1 generation were all tall
the f2 generation showed a mix of tall and short plants

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46
Q

what are the steps to solving genetics problems?

A
  1. choose a letter to represent the alleles (Capital = dominant, lower-case = recessive)
  2. the phenotype is the characteristic you see
  3. the genotype is always a pair of alleles (two letters)
  4. the gamete is always a single allele (one letter)
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47
Q

if the parent phenotypes are tall x short, give an example of the parent genotype followed by the gametes

A

TT x tt
T and T x t and t

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47
Q

describe the phenotype of F1

A

100% the dominant phenotype

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47
Q

when can an f2 cross happen?

A

when an f1 plant is self-pollinated (Selfing)

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47
Q

what is the phenotype that is expressed in the F1 generation

A

dominant

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47
Q

the dominant what is always expressed in the f1 generation?

A

phenotype

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47
Q

how do we end up with a short plant (not the dominant phenotype)?

A

both alleles have to be recessive

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47
Q

describe f1 offspring that have the genotype Tt and explain why you say this

A

heterozygous
(have 2 different alleles)

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47
Q

monohybrid ratio of an f2 cross

A

3 dominant phenotypes: 1 recessive phenotype

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48
Q

ratio of tall to short plants in an f2 cross

A

3 tall : 1 short

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49
Q

probability of tall and short plants in an f2 cross

A

75% tall
25% short

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50
Q

what is mendel’s first law also known as?

A

the law of segregation

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51
Q

give mendel’s first law in terms of genes

A

the characteristics of an organism are determined by facrors (genes) which occur in pairs. only on member of a pair of factors (genes) can be represented in a single gamete

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52
Q

which stage of meiosis creates the law of segregation?

A

metaphase 1

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53
Q

why is it metaphase 1 of meiosis that creates the law of segregation?

A

since homologous chromosomes - and hence allele pairs - are separated in meiosis 1

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54
Q

what does the law of segregation not take into account?

A

crossing over - it assumes that the alleles stay on the same chromosomes

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55
Q

how is each allele for a trait packaged following meiosis 1?

A

into a separate gamete

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56
Q

what is packages into separate gametes following meiosis 1?

A

each allele for a trait

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57
Q

monohybrid inheritance

A

the inheritance of a single gene

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58
Q

monohybrid cross

A

the inheritance of a single characteristic

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59
Q

how many characteristics are passed on during each cross and how many did mendel focus on for his experiments?

A

thousands during each cross
mendel focused on the inheritance of single characteristic in some of his experiments

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60
Q

examples of monohybrid crosses

A

flower colour
seed colour

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61
Q

what did mendel follow 2 of in some of his experiments?

A

the inheritance of 2 different characters

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62
Q

dihybrid cross

A

the inheritance of 2 different characteristics

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63
Q

example of a dihybrid cross + explain

A

seed colour and seed shape
each of these 2 genes (the gene for colour and the gene for shape) have 2 different alleles

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64
Q

how are f1 when we self-pollinate and why?

A

heterozygous since they have the genotype of both parents

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65
Q

why are f1 heterozygous?

A

they have the genotype of both parents

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66
Q

what is the ratio we get every time when we cross two heterzygotes?

A

9:3:3:1

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67
Q

when do we always get the 9:3:3:1 ratio?

A

when we cross two heterzygotes

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68
Q

how come genes assort in the gametes independently in a dihybrid cross?

A

they are on different chromsomes and independent assortment during meiosis occurs

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69
Q

how do genes assort in gametes? use the example of YyRr assorting into gametes

A

YR, Yr, yR, yr

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70
Q

how do group alleles in a dihybrid cross table?

A

group alleles of the same gene together

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71
Q

how many different possible gametes do we need to get the correct ratio in a dihybrid cross and how many squares is this in a punnet square?

A

4 different gametes
16 square punnet square

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72
Q

what is mendel’s second law of inheritance also known as?

A

the law of independent assortment

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73
Q

where do we see the chromosomal basis of mendel’s law?

A

2nd law of inheritance

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74
Q

what is mendel’s 2nd law of inheritance the basis of?

A

independent assortment in meiosis

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75
Q

what can we have because of independent assortment?

A

can have any combination of 4 alleles which will be evenly distributed

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76
Q

how come we can have any combination of 4 alleles which will be evenly distributed?

A

because of independent assortment

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77
Q

how can we prove that f1 is heterozygous? explain

A

cross the heterozygous with a homozygous recessive
the ratio of phenotypes will be 1:1:1:1
if it were homozygous, all would appear as the dominant one does

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78
Q

how many gametes are there if there’s only 2 alleles?

A

one

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79
Q

how can we determine whether the results of a cross differ significantly from the expected results?

A

can perform a statistical test known as the chi^2 test

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80
Q

how do we work out the expected numbers for the chi^2 test?

A

1 - add up each value for each phenotype
2 - divide by 16 (the number of possible results to an F1 cross)
3 - multiply the answer by the 9:3:3:1 ratio

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81
Q

what type of answers should the expected numbers come out as during the chi^2 test?

A

a similar set of results to the actual number

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82
Q

chi^2 formula

A

x^2 = sum of (O-E)^2/E

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83
Q

what is a statistical test designed for?

A

to test a null hypothesis

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84
Q

what is the null hypothesis in genetics?

A

there is no significant different between the observed and expected results

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85
Q

what does the chi^2 test test?

A

the null hypothesis of genetics

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86
Q

what do we do once we have a value for chi^2?

A

refer it to the chi^2 table

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87
Q

what do we normally have a probability level of in genetics and what does this mean?

A

5%
we can be confident to a limit of 5% that the results will be expected

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88
Q

how do we use the probability level of 5% on the chi^2 table?

A

use 0.05

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89
Q

how do we determine which degrees of freedom to use on a chi^2 table?

A

number of different categories (phenotypes) - 1

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90
Q

how do we get a critical value on a chi^2 table?

A

wherever the probability of 0.05 and the correct degree of freedom meet

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91
Q

what is the name for the value where the probability of 0.05 and the correct degree of freedom meet on a chi^2 table?

A

the critical value

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92
Q

what do we use the critical value of a chi^2 table for?

A

to decide whether we accept or reject the null hypothesis

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93
Q

how do we know whether to accept or reject the null hypothesis?

A

if out chi^2 value is below the critical value (Even by a little bit), we accept the null hypothesis

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94
Q

How do we test whether a parent has the correct genotype for breeding?

A

Cross it with a homozygous recessive

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95
Q

What is the only variety that will produce offspring with the same genotype as both parents?

A

Homozygous recessive

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96
Q

In which situation would Mendel’s principle of independent assortment hold true for all dihybrid crosses?

A

If each chromosome only had one gene locus

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97
Q

Dihybrid

A

Genes on different chromosomes

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98
Q

When does Mendel’s 2nd law apply?

A

When we’re looking at genes that are carried on different chromosomes

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99
Q

Why is Mendel’s 2nd law not perfectly applicable to reality?

A

In reality, each chromosome carries many different genes and these are inherited together during meiosis

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100
Q

Describe the genes that are on the same chromosome

A

Linked

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101
Q

When will independent assortment not separate genes?

A

If the genes we’re studying are on the same chromosome (linked)

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102
Q

What do linked genes not undergo?

A

Independent assortment

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103
Q

When does no exchange occur between genes?

A

During linkage, when there are two genes on a single pair of homologues

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104
Q

How many gametes can we get if genes are on separate chromosomes v.s when they’re on the same chromosome?

A

Separate = 4 gametes
The same = 2 gametes

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105
Q

What are the only gametes that we can get with autosomal linkage?

A

Only double dominant or double recessive

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106
Q

Autosomes

A

Non-sex chromosomes

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107
Q

The condition where genes are close together on the same chromosome

A

Linkage

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108
Q

Why can we only have double dominant or double recessive due to autosomal linkage?

A

Since these genes can’t be separated since they’re on the same chromosome

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109
Q

What are linked in some pea plants?

A

Genes for flower colour and pollen grain shape are linked

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110
Q

What are genes carried on the same if they’re linked?

A

Same autosome

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111
Q

Phenotype ratio for linked genes

A

3:1

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112
Q

What can’t we obtain when genes are linked and are on the same chromosome?

A

The usual 16 square punnet and 9:3:3:1 ratio

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113
Q

When don’t we get the usual 16 square punnet and 9:3:3:1 ratio?

A

When genes are linked (carried on the same autosome)

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114
Q

With linked genes, if we were to cross breed the parents, would we get intermediate phenotypes forming in the F2 generation?

A

Yes

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115
Q

What would we get if we were to cross breed parents that have linked genes in real life?

A

Would actually get intermediate phenotypes forming in the F2 generation even though they’re on separate chromosomes

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116
Q

Why would we get intermediate phenotypes forming in the F2 generation even though they’re on separate chromosomes if we were to cross breed parents with linked gens?

A

Due to crossing over between the homologous chromosomes

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117
Q

What is the ratio when crossing parents with linked genes when considering crossing over?

A

Still not a 9:3:3:1 ratio - closer to 3:1

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118
Q

Why is the phenotype ratio still 3:1 in the offspring of parents with linked genes when we consider crossing over?

A

Only a few of the intermediates form Because crossing over between genes is rare

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119
Q

What will most of the gametes be when crossing parents with linked genes?

A

Parental gametes

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120
Q

What are genes likely to do if they’re together on a chromosome?

A

Travel through time like this

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121
Q

Why do only a few intermediates form during the cross breeding of two parents with linked genes?

A

Because crossing over between genes is rare

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122
Q

What will most F2 phenotypes be when crossing parents with linked genes be?

A

The parental type

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123
Q

What is the small % that aren’t the parental type when crossing parents with linked genes due to?

A

Autosomal linkage

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124
Q

When does crossing over occur during meiosis?

A

Prophase I

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125
Q

What happens during crossing over of meiosis?

A

Homologous pairs of chromosomes come together and crossing over may occur between chromatids at points called chiasmata

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126
Q

Points at which crossing over occurs on homologous pairs of chromosomes

A

Chiasmata

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127
Q

What can happen if crossing over occurs between two genes?

A

It separates alleles that were previously linked and allows them to combine in new recombinant genotypes

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128
Q

Genotypes formed after crossing over between genes

A

Recombinant genotypes

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129
Q

How do recombinant genotypes form?

A

When crossing over occurs between two genes, separating alleles that were previously linked and allowing them to combine in new recombinant genotypes

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130
Q

Recombinant

A

The offspring phenotypes that are not the parental phenotypes

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131
Q

The offspring phenotypes that are not the parental genotypes

A

Recombinants

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132
Q

What for during crossing over?

A

Chiasmata

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133
Q

Points at which crossing over occurs?

A

Chiasmata

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134
Q

What is a homologous pair of chromosomes?

A

A bivalent of chromosomes in pairs

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135
Q

What form during crossing over?

A

Chiasmata

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136
Q

What will gametes contain following crossing over?

A

The single chromosomes

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137
Q

When are genes less likely to form recombinant chromosomes?

A

When they’re closer

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138
Q

What are closer genes less likely to form?

A

Recombinant chromosomes

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139
Q

When is the frequency of recombination low?

A

When genes are closer together

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140
Q

What are there more of with further apart genes and why?

A

More recombinant gametes since there are more opportunities for crossing over

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141
Q

When are the more recombinant gametes due to more opportunities for crossing over?

A

When we have further apart genes

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142
Q

What do more recombinant gametes lead to?

A

More offspring with recombinant phenotypes

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143
Q

What are unexpected combinations of phenotypes due to?

A

Genes being linked

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144
Q

What is responsible for less frequent phenotypes?

A

Crossing-over

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145
Q

What do linked genes lead to?

A

Unexpected combinations of phenotypes

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146
Q

What is a common explanation for rejecting a null hypothesis in a genetics experiment?

A

Linked genes

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147
Q

What are linked genes a common explanation for?

A

Rejecting a null hypothesis in a genetics experiment

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148
Q

If we have a pattern that doesn’t follow the 9:3:3:1 ratio, what is likely to be down to?

A

Autosomal linkage

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149
Q

what is codominance?

A

Codominance refers to inheritance patterns when both alleles in a heterozygous organism are equally expressed

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150
Q

What is it called when we have inheritance patterns where both alleles in a heterozygous organism are equally expressed?

A

Codominance

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151
Q

Examples of codominance

A

Coat colour in horses and cattle
Blood groups in humans

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152
Q

Explain codominance in horses and cattle

A

Red cot colour is co-dominant to white coat colour. Animals that are heterozygous are roan-coloured (red hair interspaced with white hair - not pink hair)

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153
Q

Explain codominance in human blood groups

A

The blood group AB is the result of two alleles, A and B, both being equally expressed in the phenotype, neither being dominant to the other

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154
Q

Which alleles are expressed equally in the phenotype with human blood groups and why?

A

A and B since neither are dominant to the other (codominance)

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155
Q

Which human blood group is recessive?

A

O

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156
Q

What are the codominant human blood groups and what are the recessive blood groups in humans?

A

A and B —> codominant
O —> recessive

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157
Q

Possible genotypes of blood type A

A

AA or AO

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158
Q

Possible genotypes of blood type B

A

BB or BO

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159
Q

Genotype of blood type AB

A

AB

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160
Q

Genotype of blood type O

A

OO

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161
Q

What do the sex chromosomes comprise of for females?

A

2 X chromosomes

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162
Q

What do the sex chromosomes comprise of for males?

A

X and Y

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163
Q

How is the X chromosome different to the Y chromosome?

A

The X chromosome is much longer than the Y chromosome

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164
Q

Why are sex linkage conditions more common in males?

A

Because the X chromosome is much longer than the Y chromosome

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165
Q

Explain why sex linkage conditions are more common in males due to the X chromosome being much longer than the Y chromosome

A

Because the X chromosome is larger, it carries more genes
If there’s a defective gene on the X chromosome, there’s no corresponding gene on the y-axis to cancel it out - the deflective gene isn’t counteracted by another dominant gene

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166
Q

Where are sex linked recessive alleles carried?

A

On the X sex chromosome

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167
Q

What are carried on X chromosomes?

A

Sex linked recessive alleles

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168
Q

When a sex linked recessive alleles expressed in females?

A

If both X chromosomes carry the allele (homozygous recessive)

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169
Q

Why are sex linked recessive alleles always expressed in males?

A

Since the Y chromosome does not have a homologous locus for the gene - there’s no second allele to be dominant over it

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170
Q

Example of a sex linked condition

A

Haemophilia

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171
Q

What is haemophilia an example of?

A

A sex linked condition

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172
Q

What is the haemophilia gene?

A

An X-linked recessive gene

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173
Q

Give an example of an X-linked recessive gene

A

The haemophilia gene

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174
Q

Unaffected carrier of haemophilia mother genotype

A

X^HX^h

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175
Q

Haemophilia gene notation

A

X^h

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176
Q

Unaffected by haemophilia father genotype

A

X^Hy

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177
Q

Give the genotypes for the following (haemophilia):
Unaffected son
Unaffected daughter
Affected son
Unaffected carrier daughter

A

X^Hy
X^HX^H
X^hy
X^HX^h

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178
Q

If women have one dominant copy of the normal allele, are they affected by haemophilia?

A

No

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179
Q

What does it take for a male to be affected by haemophilia? Why?

A

Have one copy of the recessive gene
There’s nothing along the y-chromosome to cancel it out

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180
Q

Describe the percentages and ratios when crossing a normal male and a carrier female of haemophilia

A

25% carrier female
25% normal female
25% normal male
25% haemophiliac male

1:1:1:1

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181
Q

What is sex linkage different to?

A

Autosomal linkage

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182
Q

Explain what haemophilia is and what it does

A

Is an example of a sex linked condition
Affects the clotting of the blood
Blood doesn’t clot effectively with this genotype and there’s a risk of internal bleeding and bleeding around the joints

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183
Q

How can we show how a condition has been carried forward through the generations?

A

Use a pedigree chart

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184
Q

Pedigree chart

A

A chart that diagrams the inheritance of a trait or health condition through generations of a family

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185
Q

What did a pedigree chart prove for the royal family?

A

That haemophilia was carried down through the generations

186
Q

What is the most reliable form of DNA evidence?

A

Mitochondrial DNA

187
Q

Why is mitochondrial DNA the most reliable DNA evidence?

A

We inherit mitochondria from our mothers. It’s the mitochondria from the oocyte (not sperm) that ends up in the embryo.

188
Q

Which mitochondria do embryos inherit?

A

The mitochondria from the oocyte, not the sperm

189
Q

2 examples of sex linked conditions

A

Haemophilia
Duchenne Muscular Dystrophy (DMD)

190
Q

What does DMD stand for?

A

Duchenne muscular dystrophy

191
Q

What is DMD caused by?

A

A sex linked recessive allele of a gene that codes for the protein dystrophin

192
Q

What is dystrophin?

A

A component of a glycoprotein that stabilises the cell membranes of muscle fibres

193
Q

When do symptoms of DMD begin?

A

At a young age of around 2-3 years

194
Q

Symptoms of DMD

A

Loss of muscle mass
Progressive muscle weakness

195
Q

How is DMD inherited?

A

In the same way as haemophilia

196
Q

Chance of having a son with DMD from a healthy father and a healthy carrier mother

A

1/4

197
Q

What has been developed to help us treat DMD? Explain

A

Advances in gene therapy have meant that we can introduce healthy genes and molecular patches to repair the affected gene so that it produces a more healthy protein

198
Q

What are the conditions that are not sex linked?

A

Autosomal

199
Q

How are autosomal conditions different to sex linked conditions?

A

Will show a different pattern of inheritance

200
Q

How can we indicate whether a condition is sex linked or autosomal and whether it is the result of a dominant or recessive allele?

A

Using pedigree diagrams/charts

201
Q

How can you tell that a condition is sex linked from a pedigree diagram?

A

Since it will only occur in males, with the females either being carrier or unaffected

202
Q

Describe the females in sex linked conditions

A

Carriers or unaffected

203
Q

What type of condition only occurs in males?

A

Sex linked conditions

204
Q

What are the two possible types of autosomal conditions?

A

Autosomal dominant
Autosomal recessive

205
Q

Autosomal dominant condition

A

Only 1 copy of the harmful energy is needed to be affected

206
Q

Autosomal recessive condition

A

Have to have 2 copies of the harmful gene to be affected by the condition

207
Q

When is it not possible to determine the genotype of someone in the case of sex linked conditions? Why?

A

If a female child doesn’t have a child
We can’t determine whether they were homozygous and completely unaffected by the condition or were heterozygous (a carrier of the condition)

208
Q

What was used to treat DMD before gene therapy?

A

Viruses

209
Q

Problems with using a virus to treat a condition like DMD?

A

Cause immune responses against the virus
Virus can cause infection
Virus may affect other genes

210
Q

Mutation

A

A change in the amount or the arrangement of the genetic material (DNA or RNA) in a cell

211
Q

Describe mutations

A

Spontaneous random events

212
Q

How are mutation rates usually?

A

Very low

213
Q

In what situation are mutation rates higher?

A

In organisms with short life cycles and more frequent cell division, the rate of mutation is higher

214
Q

What’s a good thing about mutations?

A

Mutations are the source of genetic variation which can result in evolution through natural selection

215
Q

When exactly do most chromosomal mutations occur?

A

During crossing over prophase-I of meiosis or as a result of a non-disjunction during anaphase-I or anaphase-II of meiosis

216
Q

Are mutations more likely in sperm cells or egg cells?

A

Sperm cells

217
Q

Why are mutations more likely in sperm cells than in egg cells?

A

Since sperm cells are continuously produced during the life of the male
They’re therefore constantly dividing through mitosis and meiosis and mutations usually occur when DNA is copied for cell divisions

218
Q

When do mutations usually occur?

A

When DNA is copied for cell divisions

219
Q

At which stage of a male’s life are the chance of mutations even higher and why?

A

Older males
Since sperm cells are produced at an even higher rate than usually in older males, therefore there’s a higher chance of mutations

220
Q

What’s more likely to mutate - DNA or RNA and why?

A

RNA
RNA is less stable than DNA

221
Q

Why was Covid constantly mutating to produce new variants?

A

Since it was a virus and viruses only contain RNA, which is less stable than DNA and so is more likely to mutate

222
Q

What is the only thing that viruses contain?

A

RNA (no DNA)

223
Q

What does a mutation change in an organism?

A

The volume, arrangement or structure in the DNA of the organism

224
Q

What can mutations affect?

A

A single gene or a whole chromosome

225
Q

List the ways in which mutations can happen

A

Gene or point mutation
Chromosome mutation
Aneploidy
Polyploidy

226
Q

What are the most common types of mutations that can happen?

A

Gene mutations

227
Q

What is a gene mutation also known as?

A

A point mutation

228
Q

What is a gene/point mutation?

A

A change in a single nucleotide (a single letter in the genetic code)

229
Q

List the types of gene mutations

A

Addition (or insertion)
Subtraction (or deletion)
Substitution
Duplication
Inversion

230
Q

Addition (or insertion) gene mutations

A

A base is added

231
Q

What happens is an addition gene mutation happens in 3 places?

A

An extra amino acid is added to the polypeptide chain at translation

232
Q

Subtraction (or deletion) gene mutations

A

A base is deleted

233
Q

What happens if a subtraction gene mutation happens in 3 places?

A

The polypeptide has one fewer amino acids when translated

234
Q

Substitution gene mutation

A

A different base is incorporated

235
Q

Duplication gene mutation

A

The same base is incorporated twice

236
Q

Inversion gene mutation

A

Adjacent bases on the same DNA strand exchange position

237
Q

What is it called when Adjacent bases on the same DNA strand exchange position?

A

Inversion (type of gene mutation)

238
Q

What types of gene mutations are frame-shift mutations?

A

Addition and subtraction point mutations

239
Q

What are addition and subtraction point mutations examples of?

A

Frame shift mutations

240
Q

What happens during frame-shift mutations?

A

All codons after the mutation will be affected

241
Q

What happens as a result of frame-shift mutations?

A

All codons after the mutation will be affected so every amino acid in the polypeptide from the mutation onwards will be affected

242
Q

Explain why frame-shift mutations can have big effects on the shape of proteins

A

In frame-shift mutations, all codons after the mutation will be affected. As a result, every amino acid in the polypeptide from the mutation onwards will be affected. Changing even one amino acid in the polypeptide can have a big affect on the final protein structure. For example, when going from one amino acid to a chemically different one, such as from polar to non-polar, it will have a big effect on the folding of the protein.

243
Q

Why would changing an amino acid in a polypeptide sequence change the structure of a protein?

A

For example, when going form a polar to a non-polar amino acid, it will have a big effect on the folding of the protein

244
Q

Explain how frame shift mutations occur during subtraction mutations

A

Since all of the bases shift to the left as we can’t have a gap

245
Q

Explain how frame shift mutations occur during addition mutations

A

Since all of the bases move to the right from where the new bases is added, affecting every codon after the mutation

246
Q

What are the 4 different effects of single base mutations in DNA code?

A

Silent
Missense
Nonsense
Read through

247
Q

What do silent mutations usually involve?

A

The last letter of the codon

248
Q

Explain what silent mutations are and how they come about

A

Since the genetic code is a degenerate code (more than one codon per amino acid), some mutations may not actually affect the amino acid formed. So, it’s a silent mutation since the same amino acid is generated.

249
Q

How can the genetic code be described?

A

A Degenerate code

250
Q

Why is the genetic code described as a degenerate code?

A

Since there’s more than one codon per amino acid

251
Q

What is a silent mutation?

A

When the change in DNA from the mutation forms the same amino acid (since the genetic code is a degenerate code)

252
Q

Missense mutations

A

A mutation that changes the amino acids that are incorporated into a protein

253
Q

The mutation that changes the amino acids that are incorporated into a protein

A

Missense

254
Q

Nonsense mutations

A

A mutation that introduces a stop codon into the genetic code and prevents a protein from being made completely. A shorter polypeptide forms as a result.

255
Q

The mutation that introduces a stop codon into the genetic code and prevents a protein from being made completely

A

Nonsense

256
Q

What forms as a result of a nonsense mutation?

A

A shorter polypeptide

257
Q

Read through mutation

A

A mutation that converts a normal stop codon into an encoding amino acid, so the polypeptide gets too long

258
Q

The mutation that converts a normal stop codon into an encoding amino acid, so the polypeptide gets too long

A

Read through

259
Q

What happens as a result of a read through mutation?

A

The polypeptide gets too long

260
Q

Mutation that ends up producing the same amino acid

A

Silent

261
Q

What do all of the effects of single base mutations in the DNA code all change?

A

The nature of the polypeptide and the protein formed

262
Q

What will an affected mother have in her genotype for a dominant autosomal condition?

A

Only one harmful gene

263
Q

What will an affected mother have in her genotype for a recessive autosomal condition?

A

Two harmful genes

264
Q

If the cross is autosomal recessive and both parents have the condition, describe the children

A

All affected

265
Q

Why will not all of the children be affected by an autosomal dominant cross of two affected parents?

A

Since for the offspring we use the usual method where we need two copied of the harmful gene for the female to be affected, even if it’s a dominant autosomal cross initially

266
Q

Why is a different protein formed when a mutation occurs?

A

Due to a change in the genetic code

267
Q

Why are frame shift mutations often fatal for the cell?

A

The protein structure can change so much that it no longer functions

268
Q

What are frame shift mutations fatal for?

A

The cell

269
Q

When can homologous pairs of chromosomes form?

A

When you have even numbers of chromosomes

270
Q

What can form once homologous pairs of chromosomes have formed?

A

Viable gametes

271
Q

What are able to form if you have even numbers of chromosomes?

A

Homologous pairs of chromosomes

272
Q

What do all mutations do and why?

A

Change the nature of the polypeptide and the protein formed due to a change in the genetic code

273
Q

What type of mutation synthesises the dystrophin protein? How do you know this?

A

The nonsense mutation
It isn’t long enough

274
Q

What is the issue when a nonsense mutation occurs in the dystrophin protein?

A

It isn’t long enough

275
Q

What can be done about the distrophin protein not being long enough due to a nonsense mutation?

A

Gene therapy can lead to a ribosome making a longer protein

276
Q

Which stage of protein synthesis is affected most by mutations?

A

Translation

277
Q

What would happen if a mutation happened during transcription?

A

It wouldn’t occur again and again

278
Q

Explain what will happen if DNA is changed by a mutation during replication

A

It will change the base sequence and this will be copied every time transcription happens into the mRNA. This will be copied into translation.

279
Q

Where else can mutations happen aside from genes?

A

Introns

280
Q

How come mutations in introns are more common than we think?

A

It would have no affect on the protein structure

281
Q

Why do base sequences vary more in introns?

A

They are not always corrected by proof-reading systems
Mutations occur more frequently

282
Q

Why do mutations occur more frequently in introns than in genes?

A

Since they’re not always corrected by proof-reading systems

283
Q

What can mutations affect?

A

Protein synthesis

284
Q

What can mutations affecting protein synthesis change?

A

The phenotype of an organism

285
Q

Do all mutations affect the phenotype?

A

No

286
Q

What do gene(point) mutations affect?

A

A single base in a gene

287
Q

What do chromosomal mutations affect?

A

Many genes

288
Q

2 words to describe mutations

A

Random
Spontaneous

289
Q

What do mutagens do?

A

Make mutations more likely

290
Q

Whatis increased by mutagens?

A

The rate of mutation

291
Q

Give examples of mutagens

A

Ionising radiations - gamma radiation, UV, X-rays
Certain chemicals - polycyclic hydrocarbons in cigarette smoke, chemicals in air pollution

292
Q

Explain why mutagens increase the rate of mutation

A

Since they damage the DNA, and as the cell repairs the DNA, mutations can happen. The more damage to DNA caused by mutagens the more likely mutations are to happen.

293
Q

Carcinogens

A

Mutagens that increase the likelihood of the development of cancer by affecting genes that lead to the formation of cancers

294
Q

What does cancer rise from?

A

DNA mutations in cells

295
Q

How do carcinogens increase the likelihood of the development of cancer?

A

By affecting genes that lead to the formation of cancers

296
Q

What can cause DNA mutations?

A

Heredity
Radiation or chemicals
Spontaneous errors during DNA duplication

297
Q

Cancer

A

Cells which divide uncontrollably through mitosis and form a tumor

298
Q

How does a cancer spread?

A

The cells can break away and travel to other parts of the body via the lymphatic system

299
Q

What happens every time a cancerous cell divides?

A

Forms genetically identical offspring

300
Q

What has to occur for a normal cell to turn into a cancerous cell?

A

A mutation has to occur in specific genes that are involved in cell division, which are tumor suppressor genes and proto-oncogenes

301
Q

Types of genes that a mutation has to occur in in order for a normal cells to turn into a cancerous cell

A

Tumor suppressor genes
Proto-oncogenes

302
Q

What do tumor suppressor genes do?

A

Code for proteins that stop the cell from dividing in an uncontrolled way

303
Q

What has to happen to tumor suppressor genes for a cancer to form?

A

Have to be switched off

304
Q

What has to happen to proto-oncogenes for a cancer to form?

A

Be switched on

305
Q

What happens when proto-oncogenes are switched on and what does this do?

A

The proto-oncogenes become oncogenes, which stimulate the cell to divide in an uncontrolled way

306
Q

How do oncogenes form and what do they do?

A

When proto-oncogenes are switched on, they form oncogenes
Oncogenes stimulate the cell to divide in an uncontrolled way

307
Q

Which two conditions have to be met for a cell to become cancerous?

A

Both the tumor suppressor genes need to be switched off and the proto-oncogenes need to be switched on within the same cell

308
Q

Within what do both the tumor suppressor genes need to be switched off and the proto-oncogenes need to be switched on for a cancerous cell to form?

A

Within a cell

309
Q

What do we need a mutation in both of for a cancer to form?

A

Tumor suppressor genes
Proto-oncogenes

310
Q

Are very specific conditions needed for a normal cell to turn into a cancer cell?

A

Yes

311
Q

What happens once a cancer cell has formed?

A

Uncontrolled growth

312
Q

What do carcinogens make more likely to occur?

A

Mutations in tumor suppressor genes and proto-oncogenes

313
Q

What makes carcinogens different from mutagens?

A

They specifically effect tumor suppressor genes and proto-oncogenes

314
Q

What are mutations individual to?

A

The individual person

315
Q

How do we attempt to treat an individual with cancer effectively?

A

Samples are taken and DNA is sequenced so that treatments can be targeted for that individual to be treated effectively

316
Q

What type of condition is sickle-cell anaemia?

A

Genetic

317
Q

What does sickle-cell anaemia lead to the formation of?

A

Sickle shaped red blood cells

318
Q

Why does sickle-cell anaemia lead to the formation of sickle-shaped red blood cells?

A

Due to the structure of the haemoglobin within them

319
Q

What mutation causes sickle-cell anaemia?

A

A mutation of the gene which codes for one of the polypeptides in the haemoglobin molecule

320
Q

When do the red blood cells change shape for someone with sickle-cell anaemia?

A

Wherever there’s low O2 levels (low O2 partial pressures in a tissue)

321
Q

What shape are normal red blood cells?

A

Biconcave disc shaped

322
Q

Explain why sickle-cell anaemia is problematic

A

Capillaries in tissues are narrow, and regular red blood cells can only just fit
When they have a sickle shaped they’re less flexible and so don’t fit as easily in the capillaries
They therefore get stuck, and this affects circulation, including to major organs

323
Q

Why don’t sickle shaped red blood cells fit easily in capillaries?

A

Less flexible than with the biconcave disc shape and the capillaries are very narrow anyway

324
Q

When are red blood cells sickle shaped for anyone with sickle cell anaemia?

A

In any tissue where O2 levels are low

325
Q

What type of protein is haemoglobin?

A

Quaternary

326
Q

How many polypeptides is haemoglobin made up of? Why?

A

4
It’s a quaternary protein

327
Q

How many genes is one polypeptide coded by?

A

1

328
Q

What is the cause of sickle-cell anaemia?

A

Single base (point) mutation in the gene which codes for beta-haemoglobin (a polypeptide)

329
Q

The gene for which polypeptide in haemoglobin undergoes a mutation for someone with sickle-cell anaemia?

A

Beta-haemoglobin

330
Q

What does the mutation in beta haemoglobin’s gene lead to?

A

A change in the codon in mRNA and leads to a change in the amino acid in the polypeptide

331
Q

What leads to a change in the amino acid in the polypeptide of beta haemoglobin?

A

A mutation that changes the codon in mRNA and leads to a change in the amino acid in the polypeptide

332
Q

Which amino acid changes to what for someone with sickle-cell anaemia?

A

Valine (val) replaces glutamine (glu)

333
Q

Give an example of how a single letter change in a DNA sequence can have a big effect

A

When a single base mutation occurs in the gene which codes for beta-haemoglobin in haemoglobin and the amino acid changes from glutamine to valine

334
Q

What happens to haemoglobin because of the mutation in the beta haemoglobin polypeptide?

A

The haemoglobin molecule straightens out in low O2 levels instead of being globular

335
Q

What is haemoglobin doing to change shape for someone with sickle-cell anaemi?

A

The haemoglobin molecule straightens out instead of being globular

336
Q

Explain why exactly the red blood cell changes shape for someone with sickle cell anaemia

A

As (val) has replaced (glu), the molecule is less soluble in water (as valine is non-polar) and this is why it stretches out, making the red blood cells elongated and rigid

337
Q

Why is haemoglobin less soluble in water for someone with sickle cell anaemia?

A

As valine is non polar

338
Q

Which amino acid is non-polar and what does this do to someone with sickle cell anaemia?

A

Valine
It makes the molecule less soluble in water

339
Q

Describe red blood cells after they’re stretched out (sickle cell anaemia)

A

Elongated and rigid

340
Q

What causes red blood cells to be stretched out (sickle cell anaemia)?

A

As (val) has replaced (glu), the molecule is less soluble in water (as valine is non-polar), so the molecule stretches out

341
Q

How is the mutation for sickle cell anaemia obtained?

A

It’s inherited

342
Q

How is the mutation for sickle cell anaemia inherited?

A

It leads to the formation of a recessive allele

343
Q

What is the probability of having sickle-cell anaemia with 2 heterozygous parents

A

1/4

344
Q

Can someone be affected by sickle cell anaemia with a heterozygous genotype?

A

They can be slightly affected, with some haemoglobin being impacted

345
Q

Which part is the world is having sickle cell anaemia quite common? Why was this organically quite strange to understand?

A

In areas where malaria is common
Malaria is an infection, sickle cell is a genetic disease

346
Q

Why is it advantageous to have sickle cell in areas where malaria is common?

A

Individuals have a lower parasite count with sickle-cell since the sickle cell makes the malaria parasite less likely to reproduce

347
Q

What is the ideal scenario in terms in sickle cell anaemia in areas where malaria is common and why? What is the problem with the alternatives?

A

Being heterozygous (Aa) for sickle cell since it gives resistance to malaria without suffering from sickle cell anaemia
Homozygous dominant would make the individual more likely to catch malaria
Homozygous recessive would mean that, although the individual has protection from malaria, they have sickle-cell disease

348
Q

Give an example of when a mutation can give a selective advantage in an environment and is an example of natural selection

A

Being heterozygous for sickle cell anaemia in areas where malaria is common

349
Q

Chromosome mutations

A

Changes in the structure or number of chromosomes in cells. Happens on many genes on that section of chromosome.

350
Q

Explain how a mutation occurs and leads to a change in structure of a chromosome (chromosome mutation)

A

During prophase I of meiosis, homologous chromosomes pair and exchange material at chiasmata
Mutation arises when a chromosome does not rejoin accurately at the corresponding position on its homologous partner

351
Q

Why would a chromosome not rejoin accurately at the corresponding position on its homologous partner? (Chromosomal mutations)

A

Could be due to…
-deletion of part of a chromosome
-duplication of part of a chromosome
-inversion of part of a chromosome

352
Q

What type of chromosomal mutations only involve mutations on part of the chromosome?

A

Changes in structure

353
Q

What are mutations that cause changes in chromosome shapes as a result of?

A

Mistakes in crossing over during prophase I of meiosis

354
Q

What happens when mistakes occur in crossing over during prophase I of meiosis (chromosomal mutations)?

A

The homologous chromosomes, and therefore the gametes they are in, end up with some different genes

355
Q

What happens as a result of changes in chromosomal structure (chromosomal mutations)?

A

Each gamete may still fuse with another and produce a new individual, but further meiosis will be impossible as the mutant chromosomes will not be able to make homologous pairs at meiosis

356
Q

When are whole chromosomes involved and when are only parts of a chromosome involved in terms of chromosomal mutations?

A

Whole chromosomes —> changes in numbers of chromosomes
Parts of chromosomes —> changes in structure of chromosomes

357
Q

When are changes in chromosome number most likely to occur? Specifically?

A

During meiosis
When homologous chromosomes separate at anaphase I or when chromatids separate at anaphase II

358
Q

What is it called when a faulty spindle results in the chromosomes not being shared equally between the daughter cells?

A

Non-disjunction

359
Q

What does a faulty cell division due to a mutation lead to?

A

One of the daughter cells receives two copies of a chromosome while the other gets none

360
Q

What is Down’s syndrome caused by?

A

Chromosomal non-disjunction

361
Q

Explain how Down’s syndrome comes about

A

It occurs due to the failure of one homologous pair of chromosomes to separate during the first meiotic division (chromosomes not pulled apart during anaphase I)
There is a third copy of chromosome 21 on the Karotype

362
Q

Which chromosome is there a third copy of for someone with Down’s syndrome?

A

Chromosome 21

363
Q

Aneuploid cells

A

Cells with an extra copy or copies of one chromosome

364
Q

Cells with an extra copy or copies of one chromosome

A

Aneuploid cells

365
Q

What happens when non-disjunction happens during oogenesis (Down’s syndrome)?

A

A secondary oocyte has either no chromosome 21 (which can’t produce a viable embryo) or has 2 copies instead of 1 (which is trisomy 21 once the secondary oocyte with 2 copies has fused with a viable sperm = person with Down’s syndrome)

366
Q

What is it called when a secondary oocyte with 2 copies of a chromosome fuses with a viable sperm?

A

Trisomy

367
Q

What’s wrong with a secondary oocyte with no chromosome 21?

A

Can’t produce a viable embryo

368
Q

Monopsony

A

Refers to a missing chromosome from the typical diploid set

369
Q

Trisomy

A

Refers to an extra chromosome

370
Q

Example of trisomy

A

Down’s syndrome

371
Q

Give and explain an example of monosomy

A

In terms of sex gametes, you could get XO (only 1 X chromosome)

372
Q

Can you get XXY and XYY?

A

Yes

373
Q

What gender would the genotype XO (monosomy) be and why?

A

Still be female since there’s no Y chromosome

374
Q

Are chromosomal mutations more common in sex chromosomes or autosomes? Why?

A

More common in sex chromosomes since they have less affect on the general health of the person

375
Q

What is the cause of trisomy and monosomy?

A

Nondisjunction

376
Q

Nondisjunction

A

A mutation that occurs during meiosis I
Homologous chromosomes do not separate, which produces gametes with extra and missing chromosomes

377
Q

When does nondisjunction occur?

A

During meiosis I

378
Q

How many chromosomes does nondisjunction affect in humans?

A

Just 1

379
Q

Describe nondisjunction in meiosis I

A

Pair of homologous chromosomes fails to separate

380
Q

Describe nondisjunction in meiosis II

A

Pair of sister chromatids fails to separate

381
Q

A mutation that occurs during meiosis I. Homologous chromosomes do not separate, which produces gametes with extra and missing chromosomes.

A

Nondisjunction

382
Q

What’s the difference when it’s during the second meiotic division that chromatids don’t separate compared to when the homogenous chromosomes during meiosis I fail to separate (non disjunction)?

A

There will be fewer affected gametes when it’s the chromatids that don’t separate

383
Q

How many chromosomes does chromosomal Nondisjunction affect in some species?

A

Entire sets

384
Q

Polyploidy

A

Have several sets of chromosomes

385
Q

Policy

A

Number of chromosome sets that an individual has

386
Q

List some types of polyploidy

A

Haploid (n)
Diploid (2n)
Triploid (3n)
Tetraploid (4n)

387
Q

Example of haploids

A

Normal gametes

388
Q

Example of diploid

A

Our body cells

389
Q

Example of triploid

A

Endosperm in the seed

390
Q

Example of tetraploid

A

Wheat

391
Q

List and explain the different ways in which polyploidy can arise

A

Spindle defect - this leads to chromosomes failing to separate during anaphase I. The resulting gamete will have two copies of each chromosome instead of one. If this diploid gamete is fertilised by a normal haploid gamete, a triploid (3n) zygote results
If two diploid gametes fuse, a tetraploid (4n) zygote is produced
Endomitosis - when the chromosomes are replicated but cytokinesis does not occur, leading to tetraploid cells being formed

392
Q

Endomitosis

A

When the chromosomes are replicated but cytokinesis does not occur, leading to tetraploid cells being formed

393
Q

What is polyploidy common in?

A

Flowering plants

394
Q

Explain how a spindle defect can lead to polyploidy

A

This leads to chromosomes failing to separate during anaphase I. The resulting gamete will have two copies of each chromosome instead of one. If this diploid gamete is fertilised by a normal haploid gamete, a triploid (3n) zygote results

395
Q

What is polyploidy associated with?

A

Beneficial characteristics such as vigour and disease resistance

396
Q

Examples of polyploidy plants

A

3n seedless water melons
4n potatoes
6n wheat bread
8n strawberries

397
Q

Is polyploidy commoner in plants or animals?

A

Plants

398
Q

Why is polyploidy much commoner in plants than in animals?

A

Because plants can reproduce asexually and are often hermaphrodite so do not use chromosomes to determine their sex

399
Q

Hermaphrodite

A

Do not use chromosomes to determine their sex

400
Q

How do proto-oncogenes become oncogenes?

A

Mutate to them

401
Q

What would happen if tumour suppressor genes were switched off in all cells of the body? Explain

A

It leads to an increased risk of a tumour forming in various places
Risk of this being passed on to the next generation (since it’s in all cells, it involves gametes too)

402
Q

Why does tumour suppressor genes being switched off in all cells of the body lead to the risk of it being passed onto the next generation?

A

Since its in all cells, it involves gametes too

403
Q

What does conventional genetics show us?

A

That we inherit genes from our parents

404
Q

What are other things that can affect the phenotype of an organism apart from the genes inherited from parents?

A

Environment and lifestyle

405
Q

Can aspects in our environment and lifestyle that affect our phenotype be inherited?

A

According to epigenetics, yes

406
Q

What could the lifestyle our parents had influence?

A

The genes that have been passed on to the next generation

407
Q

What is epigenetics?

A

The study of heritable changes in gene expression without a change in DNA sequence

408
Q

The study of heritable changes in gene expression without a change in DNA sequence

A

Epigenetics

409
Q

What’s changes and what’s not with epigenetics

A

Change the phenotype without changing the genotype

410
Q

What determines which genes are turned off and which are turned on?

A

A persons DNA sequence
But also there’s another level of genetic control

411
Q

Epigenome

A

The control system that decides which genes are switched on/off in each cell

412
Q

What is the same in each of the cells in our body?

A

The genome

413
Q

What’s different in different cells of the body even though the genomes are the same?

A

Different epigenomes

414
Q

Are all embryo cells the same?

A

Yes , they’re genetically identical

415
Q

Why are embryo cells genetically identical?

A

Since they developed through mitosis

416
Q

How does a cell “know” if it’s a liver cell or skin cell or another cell?

A

Not every gene is expressed in every cell

417
Q

How are genes activated and deactivated in a cell?

A

DNA interacts with molecules in cells which can activate and deactivate genes

418
Q

Give an example of genes being switched on in some cells and switched off in others

A

Pancreas cells secrete protease. This would be pointless in any other of the body cells, so the gene is switched off in all cells except for those in the pancreas.

419
Q

When is it possible to alter DNA with epigenetics?

A

After it is replicated

420
Q

When DNA is altered after its been replicated by epigenetics, what does it not change and what does it change?

A

Does not change the base sequence of the DNA
Does interfere with the process of transcribing the gene during protein synthesis

421
Q

What does altering DNA after replication not change?

A

The base sequence of the DNA

422
Q

What does altering DNA after it’s been replicated interfere with?

A

The process of transcribing the gene during protein synthesis

423
Q

What causes epigenetic changes?

A

Increasing evidence that the environment can cause these changes

424
Q

What are epigenetic modifications caused by?

A

The epigenome

425
Q

Two main types of epigenetic modification

A

DNA methylation
Histone modifications

426
Q

What are both DNA methylation and histone modifications examples of?

A

Epigenetics modifications

427
Q

What is DNA methylation a way of doing?

A

Switching off genes

428
Q

What does DNA methylation do to genes?

A

Switches them off

429
Q

What happens during DNA methylation?

A

Methyl group added

430
Q

What does a gene still do when it’s not expressed?

A

It’s still used to make the protein and goes through transcription and translation etc, its just not expressed

431
Q

Where are methyl groups added during DNA methylation?

A

To an organic base

432
Q

What does adding a methyl group to an organic base do to it?

A

Interferes with its ability to form bonds with complementary bases

433
Q

What does DNA methylation do in terms of expression of the gene?

A

Prevents it

434
Q

Why does DNA methylation prevent the expression of genes?

A

Adding a methyl group to an organic base can interfere with its ability to form bonds with complementary bases and can therefore prevent the expression of the gene

435
Q

What happens to the ability of a cell to transcribe the gene with a methylated base?

A

It’s impaired

436
Q

What is impaired when a cell has a methylated base?

A

The ability of the cell to transcribe the gene

437
Q

When is the ability of a cell to transcribe a gene impaired?

A

With a methylated base

438
Q

What makes a gene less likely to be expressed?

A

More methyl groups

439
Q

What does more methyl groups do to a gene?

A

Makes it less likely to be expressed

440
Q

What is DNA within chromosomes wrapped around and what does this form?

A

Around histone proteins
Forms chromatin

441
Q

When does histone modification occur?

A

Following translation

442
Q

Give the ways in which histone modification occurs

A

By attaching…
An acetyl group (-CH3CO) to the amino acid lysine
A methyl group (-CH3) to lysine or arginine
A phosphate group (-PO4^2-) to serine or threonine

443
Q

Acetyl group

A

-CH3CO

444
Q

-CH3CO

A

Acetyl group

445
Q

Phosphate group

A

-PO4^2-

446
Q

PO4^2-

A

Phosphate group

447
Q

What are histone proteins used for?

A

Organising the DNA in a chromosome

448
Q

What are responsible for organising the DNA in a chromosome?

A

Histone proteins

449
Q

What happens if histone winds tighter?

A

May inhibit gene expression

450
Q

How is gene expression inhibited in terms of histone?

A

When it winds tighter

451
Q

What happens when histone winds more loosely?

A

It can increase gene expression

452
Q

When is gene expression increased by histone?

A

When it winds more loosely

453
Q

What happens to histone when the different groups mentioned are added to it?

A

It’s wound less tightly

454
Q

What happens to DNA when histone is wound less tightly?

A

DNA is less tightly coiled

455
Q

What can e done when DNA is less tightly coiled?

A

RNA polymerase is able to access the gene and it can be transcribed

456
Q

What happens when DNA is wrapped tightly around the histone?

A

It’s harder to read and therefore the gene is less likely to be expressed

457
Q

When is the gene less likely to be expressed in terms of histone?

A

When DNA is wrapped tightly around the histone

458
Q

How do we get different expression of the same gene in different parts of the same organism?

A

Different epigenetic modifications can occur in cells of the same tissue and in different tissues

459
Q

Stem cell

A

An undifferentiated cell which can develop into any type of cell in the body

460
Q

Undifferentiated cell which can develop into any type of cell in the body

A

Stem cells

461
Q

What do the stem cells of an embryo do?

A

Progressively differentiate, switching off genes coding for enzymes that are not needed

462
Q

Which cells of an embryo progressively differentiate and how?

A

Stem cells
By switching off genes coding for enzymes that are not needed

463
Q

What are the only genes that differentiated cells express?

A

The genes that are necessary for their own activity

464
Q

What type of cells only express the genes that are necessary for their own activity?

A

Differentiated cells

465
Q

Examples of differentiated cells only expressing the genes that are necessary for their own activity

A

Skin cells produce melanin but retinal cells produce Rhodopsin

466
Q

Where are retinal cells?

A

At the back of the eyes

467
Q

Cells at the back of the eyes?

A

Retinal cells

468
Q

Purpose of melanin

A

Gives in its colour and protects from UV rays

469
Q

What gives skin its colour?

A

Melanin

470
Q

What does rhodopsin do?

A

Responds to different light intensities

471
Q

What is it that retinal cells produce that responds to different light intensities?

A

Rhodopsin

472
Q

How many decimal places do we quote a chi^2 value to?

A

Match the number of decimal places used on the chi^2 table

A level Biology (26 decks)

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