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Biology Unit 4 > 📚4.3- Inheritance > Flashcards

📚4.3- Inheritance Flashcards

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1
Q

Define the term gene:

A

A sequence of DNA that codes for a polypeptide and which occupiers a specific locus on a chromosome

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2
Q

Define the term allele

A

A variant nucleotide sequence for a particular gene at a given locus, which codes for an altered phenotype

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3
Q

What a determines the structure and functions in living organisms

A

Polypeptides and proteins and :: the genes which codes for the sequences of DNA

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4
Q

How many alleles May a gene have?

A

A single gene may have one, two or many alleles.

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5
Q

How many genes control coat colour in dogs.

A

MANY
E.g in one the nucleotide sequence codes for an enzyme that makes the fur black, but a small difference gives a slightly altered pigment molecule that makes the fur brown.

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6
Q

Describe the relationship between genes and alleles

A

A gene controls a characteristic and allele are different versions of the gene

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7
Q

Give some examples of genes and alleles in humans

A

Gene: number of fingers
Allele: 5;6

Gene: freckles
Allele: present; absent

Gene: Rhesus blood group
Allele: positive; negative

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8
Q

Give some examples of genes/alleles in a sweet pea

A

Gene: height
Allele: tall; dwarf

Gene: seed colour
Allele: yellow; green

Gene: flower position
Allele: terminal; axial

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9
Q

What genes does a diploid individual have?

A

They have one chromosome from each parent and :: one copy of each gene from each parent.

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10
Q

What’s homozygous for a gene mean?

A

When the alleles of a particular gene are the same from both parents.

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11
Q

What’s heterozygous for a gene mean?

A

If the alleles of a particular gene are different for both parents an individual is heterozygous for that gene.

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12
Q

What is a genotype?

A

All of the alleles of a gene that an individual contains

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13
Q

What is a phenotype?

A

The characteristic shown in an individual e.g brown hair, blue eyes

It is the expression of the genotype in a specific environment

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14
Q

What is a dominant allele?

What is it represented by?

A

It is an allele that is always expressed when it is present.

It is represented by a capital letter.

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15
Q

What is a recessive allele?

What is it represented by?

A

A recessive allele is only expressed when it is homozygous.

It is represented by a lower case letter.

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16
Q

What is monohybrid inheritance? Give examples.

A

It is the inheritance of a single gene, such as that controlling plant height or seed colour.

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17
Q

Describe Gregor Mendels experiments to investigate monohybrid inheritance

A

He studies inheritance in plants of the garden pea, because of their agricultural importance there were several varieties that were true breeding.
Mendel chose pairs of peas with contrasting characteristic (e.g tall plants and short plants) and found that characteristics are:
-controlled by single genes
-controlled by genes in different chromosomes
-clear-cut and easy to tell apart

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18
Q

Why were peas a good subject matter for Gregor Mendel?

A

1) they are easy to grow
2) their flowers can self-fertilise and cross fertilise
3) they make flowers and fruit in the same year
3) they make a large number of seeds from each cross (f1 and f2 phenotypes can be counted and :: have statistical meaning).

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19
Q

Name a use for peas (link to another topic)

A

Peas have been used in crop rotation in Europe since the 8th centuary to increase nitrate levels in the soil.

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20
Q

What does a diagram of a genetic cross show?

A

1) the generations e.g parents, F1 and F2
2) the genotypes of parents and offspring
3) the phenotypes Of parents and offspring
4) the alleles present in the gametes
5) the symbols for the alleles are defined

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21
Q

What does F1 stand for?

A

First Filial generation (the offspring of the parents of the cross).

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22
Q

What does F2 stand for?

A

Second filial generation (the offspring of a self fertilised F1 plant it if a cross between members of the F1 generation.

The grandchildren if the original parents.

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23
Q

What are the rules for a monohybrid cross?

A
  • The gene has two alleles e.g T for tall and t for short

- If both parents are homozygous, you take one allele from each parent to determine the offspring genotype

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24
Q

In a monohybrid cross, what will 2 heterozygous individuals produce?

A

An offspring of a phenotypic ration of 3

With dominant characteristic) to 1 (with recessive characteristic

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25
Q

Define the terms test cross/back cross

A

It is a cross between an individual with the same phenotype if the dominant characteristic, but unknown genotype, with an individual that is homozygous recessive for the gene in question.

It shows if a dominant characteristic is determined by one or two dominant alleles

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26
Q

What two genotypes May an organism that is dominant for a characteristic have?

A

May be homozygous dominant or heterozygous

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27
Q

What are the expected results for a tes cross if the organism in question was heterozygous for a characteristic?

A

As you make the cross with a known homozygous recessive organism one of the F1 would show the dominant characteristic e.g the tall Tt plant, but the other would show the recessive characteristic e.g tt dwarf plant in a 50:50 ratio.

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28
Q

What happens in co-dominance?

A

Both alleles of a gender are expressed, the heterozygotes phenotype shows the phenotype of both heterozygotes e.g the production of a speckeled hen from a black feathered chicken and a white feathered chicken.

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29
Q

What is incomplete dominance?

A

It is the expression of a heterozygotes phenotype as something between the two parental phenotype e.g white flowers and red flowers give Pjnk F1.

Neither of the phenotypes for each parent is fully expressed

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30
Q

What results would you expect if you were to cross two co-dominant species

A

The F2 generation would have the ratio 1: 2: 1, with the 1’s showing the original parental phenotypes and the 2 showing the co-dominant colouring.

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31
Q

What was mendels first law?

A

The law of segregation which states “the characteristics of an organism are determined by factors (alleles) which occur in pairs. Only one pair is present in each gamete.

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32
Q

What is independent assortment?

A

The mixing of maternal and paternal alleles in any combination in gametes.

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33
Q

What are unlinked genes

A

Genes that behave independently in relation to eachother.

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34
Q

What is dihybrid inheritance?

A

The simultaneous inheritance of two unlinked genes I.e genes on different chromosomes.

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35
Q

What is the expected ratio of offspring in a dihybrid heterozygous cross?

A

Offspring ratio:

9:3:3:1

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36
Q

How do you calculate the ratio of progeny?

A

The total number of offspring for a specific characteristic e.g round yellow bean is divided by the number of homozygous recessive individuals.

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37
Q

The formulation of the dihybrid ratio (9:3:3:1) led to mendels second law, what is it?

A

“Either one of a pair of contrasted characters may combine with either of another pair”

Meaning, each member of a pair of alleles May combine randomly with either of another pair on a different chromosome.

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38
Q

How does a dihybrid rest cross work?

A

You test the dihybrid genotype by crossing it with an individual that is homozygous recessive for both genes e.g rryy. The ratios of the phenotypes in the progeny indicate the genotype if the parent.

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39
Q

Define the term linked gene

A

It is the description of genes that are on the same chromosome and therefore do not segregated independently at meiosis.

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40
Q

Why does gene linkage occur?

A

The alleles of two genes that are on the same chromosome can’t segregated independently (can’t move to opposite poles of the cell at meiosis) because they are in the same physical structure, the chromosome, so they must move together.

(Diagram of 202)

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41
Q

What is the name for genotypes that are present in the offspring and are identical to a parent

A

Parental genotype

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42
Q

What is the name of new genotypes found in offspring due to independent assortment?

A

Recombinant genotypes

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43
Q

Why is Mendelians ratio incorrect when apply it in real life?

A

Crossing over is more rare than predicted and :: the majority of gametes would be parental as the number of gametes with different genotypes are not equal.

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44
Q

What determines the values of crossing over between chromosomes?

A

The further apart two genes are on a chromosome the more opportunity there is for a crossover to occur between them.
This leads to more recombinant gametes and :: more offspring with recombinant offspring.

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45
Q

How do you identify if genes are linked based on offspring?

A

If the numbers of progeny with different combinations of characteristics do not correspond with Mendelian ratios.

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46
Q

What is a common explanation for rejecting the null hypothesis?

A

If the numbers of progeny with different combinations of characteristics do not correspond with Mendelian ratios.

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47
Q

How do you calculate the crossover value?

A

The number of recombinants/number of progeny x100

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48
Q

What is the probability rule of addition?

A

The probability of all scenarios = 1

E.g probability of getting heads when flipping a coin= 1/2 and tails= 1/2

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49
Q

What is the probability rule of multiplication?

A

The probability of two events happening is their individual probabilities multiplies e.g two heads in a row = 1/2 x 1/2 = 1/4

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50
Q

When is the chi squared test used?

A

It is used to test if the numbers of different phenotypes are close enough to the predicted values to support the genetic explanation of how they arose.

If the numbers are not close enough this test tells us that they have arisen for another reason.

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51
Q

What is the null hypothesis?

A

It is a statement which states that there is no difference between the observed and expected results of a cross.

The observed results are due to Mendelian inheritance and that any deviation from the expected ratio is due to chance.

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52
Q

Why can the null hypothesis exist?

A

It is based on the Mendelian inheritance which states that there is no difference in:

  • the number of the different types of gamete
  • the probability of each gamete type fusing with another type of gamete
  • the viability of the embryos whatever their genotype -the genes are not linked
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53
Q

What are degrees of freedom?

A

The measure of the number of values that can vary independently.
In the analysis of crosses it is one less than the number of classes of data.

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54
Q

What is the critical point?

A

5% or 0.05 on a table of results

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55
Q

What points should you consider when constructing a conclusion for a chai squared test?

A
  • what the calculated value of X2 is
  • whether this is more or less than the critical value (and state this value)
  • whether you accept or reject the null hypothesis
  • what critical value is e.g 5%
  • whether the inheritance in Mendelian or not
  • what the deviation is caused by (chance or linked genes).
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56
Q

What are the three main angiosperm species?

A

Hermaphrodite
Monoecious
Dioecious

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57
Q

What are hermaphrodites?

A

Angiosperms which make both pollen and ovules

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58
Q

What are monoecious plants?

A

Angiosperms which have separate Male and female flowers on the same plant e.g maize

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59
Q

What are dioecious plants?

A

Plants that have separate Male and female individuals e.g holly

60
Q

Give some examples of hermaphrodites in animals

A

E.g the garden snail in the phylum mollusca or the earthworm in the phylum Annelida, it’s they are rare.

61
Q

What factors can control whether an individual animal is male or female?

A

1) temperature: crocodile/lizard eggs hatch as Male when the temperature is above 32 degrees and female when it’s below
2) sequential hermaphroditism (a mollusc makes a stacks individuals where those at the top are male and bottom are female)
3) clownfish hierarchies: when the dominant female dies the dominant male changes sex and takes her place
4) the male sludge work can become a hermaphrodite and fertilise itself if females are not available
5) chromosome structure: in mammals females have two X chromosomes, males have an X and a Y chromosome. It is the opposite in birds

62
Q

What does karyotype analysis enable scientists to do?

A

It allows medical geneticist is to determine if an individual has an abnormality in their chromosome number, or in some cases structure.

63
Q

How many chromosomes do human cells contain?

A

46 chromosomes, 23 from each parent

64
Q

How are the chromosomes from each parent arranged?

A

They are arranged in homologous pairs with each pair containing two chromosomes of the same size and shape, with genes in the same order coding for the same characteristics.

Each homologous pair has one chromosome from each parent.

65
Q

What is a karyotype?

A

The arrangement of homologous Paris in decreasing size order.

66
Q

What are the autosomes?

A

22 homologous pairs of chromosomes with identical genes (may have different alleles).

67
Q

What are heterosomes?

A

The 23rd pair of chromosomes in a human cell where there’s either two X chromosomes or one X and one Y chromosome.
The Y chromosome is much shorter.
They are heterosomes because the sex chromosomes are different sizes.

68
Q

What are the pseudoautosomal regions (PAR1 and PAR2)

A

Two regions on the human X and Y chromosomes which are homologous and :: can pair with eachother at meiosis.

69
Q

What do the pseudoautosomal regions on the sex chromosomes (PAR1 and PAR2) reflect?

A

They reflect the evolutionary loss of genes from one sex chromosome, leaving the larger X and smaller Y chromosome which exists now.

70
Q

Why are females considered the homogametic sex?

A

Because their gametes are identical with respect to sex chromosomes as all female secondary oocytes contain an X chromosome.

71
Q

Why are males considered the heterogametic sex?

A

Because at meiosis I am X chromosome passes into one secondary spermocyte and a Y chromosome passes onto the other causing half of the males spend to contain an X chromosome and the other half to contain a Y chromosome.

72
Q

What maintains the fact that there is equal chance of the foetus being Male of female.

A

At fertilisation the oocyte May be fertilised by either an X or Y carrying sperm with equal probability.

73
Q

Name a gene that the Y chromosome possess which the X doesn’t, explain its significance.

A

The SRY gene or ‘sex determining region in the Y chromosome’ gene which is responsible for switching on genes on other chromosomes e.g genes on the autosomes which are responsible for the expression of male characteristics.

74
Q

Compare the relative size of X and Y chromosomes

A

The X chromosome is much larger than the Y chromosome and is only homologous with the Y chromosome at the tips.

75
Q

Define the term carrier

A

A phenotypically normal female with one normal, dominant allele and one mutant recessive allele

76
Q

Define the term sex linkage

A

A gene is carried by a sex chromosome so that a characteristic it encodes is seen predominantly in one sex.

77
Q

What chromosomes are the only chromosomes to carry genes?

What does this mean?

A 
X chromosomes (not Y chromosomes)
This means that females have two copies of each gene  x males have only one copy.

As a result If a female is heterozygous for one of those genes the dominant allele will be expressed as normal.
Whichever allele the Male carries is expressed and :: if he carries a recessive allele e.g for haemophilia, he will be a haemophiliac.

78
Q

What is an example of a sex-linked condition

A

Haemophilia

79
Q

What is an example of a sex linked gene?

A

A gene on a chromosome that gives rise to a sex linked condition

80
Q

Why is the recessive allele on the X chromosomes of males always expressed?

A

Because they do not carry a corresponding dominant allele.

81
Q

What should you make sure you do when quoting phenotypic ratios for sex linked conditions?

A

Always state the ratios for sons and daughters separately as they are affected differently.

82
Q

How do you represent genetic inheritance of possible sex linked diseases?

A

On pedigree diagrams

83
Q

What are pedigree diagrams used for?

A
  • used to estimate the probability of a child inherited genetic conditions e.g. DMD
  • Used to predict the probability of developing conditions that may be reduced by lifestyle choices e.g. heart disease
84
Q

What is the mutation?

A

A mutation is a change in the amount, arrangement or structure in the hereditary material of an organism, either DNA or, in the case of some viruses, RNA.

85
Q

What are mutation is described as?

A
  • Spontaneous, as there may happen without an apparent cause.
  • Random, as they appear to happen with equal probability anywhere in the genome of diploid organisms.
86
Q

Where can mutations occur?

A

Mutations can occur in all cells (somatic cells), but only mutations that occur and gametes can be inherited.

87
Q

Are mutations harmful or beneficial?

A
  • Most mutations are harmful e.g. exposure to UV light is linked to mutations resulting in skin cancer.
  • Some mutations are beneficial and although rare they give an individual a selective advantage.
88
Q

What organisms show a greater rate of mutation? Why?

A

Organisms with a short lifecycles and frequent meiosis show a greater rate of mutation than others because mutations occur during DNA replication prior to cell division.

89
Q

What can increase mutation rates?

A

1) Ionising radiation, e.g. gamma rays, x-rays and UV lights.
2) Mutagenic chemicals e.g. the polycyclic hydrocarbons in cigarette smoke, methanol, mustard gas.

90
Q

How does ionising radiation cause mutations in cells?

A

Radiation joins adjacent pyramid in bases in DNA strand so that at replication, DNA polymerase may insert an incorrect nucleotide.

91
Q

Why is UV radiation particularly dangerous in causing mutations?

A

UV light of wavelength 260 nm is particularly mutagenic as it is the wavelength of DNA absorbs most efficiently.

92
Q

Why are some chemicals such as acridine mutagenic?

A

They have flat molecules which can slide in between base pairs in the double helix and prevents DNA polymerase inserting the correct nucleotide at replication.

93
Q

In what ways can mutations occur?

A

1) Gene or point mutation
2) chromosome mutation
3) aneuploidy
4) polyploidy

94
Q

How does Gene or point mutation work?

A

DNA is not copied accurately in the S phase, before cell division. These errors involve one or more small number of bases.

95
Q

How do chromosome mutations work?

A

Chromosomes may get damaged and break. Broken chromosomes may repair themselves on the DNA and protein rejoin.
They may not repair themselves correctly, altering the structure and potentially affecting a large number of genes.

96
Q

How does aneuploidy work?

A

A whole chromosome may be lost or added, In non-disjunction when chromosomes fail to separate to the polls of dividing cells at anaphase I or when chromatids fail to separate at anaphase II.

97
Q

How does polyploidy cause mutations?

A

The number of chromosomes may double if the cell fails to divide following the first nuclear division after fertilisation.

98
Q

What in bacteria makes genes on the bacterial chromosome more likely to be mutated?

A

Mutator genes

99
Q

Give 5 examples of gene (point) mutations.

A

1) Addition- a base is added. If this happens in 3 places an extra amino acid is added to the polypeptide chain at translation.
2) Duplication- the same base is incorporated twice.
3) Subtraction- a base is deleted. If this happens 3 times the polypeptide has one fewer amino acids when translated.
4) Substitution- a different base is incorporated
5) Inversions- adjacent based on the same DNA strand exchange position.

100
Q

What affects may the point mutation have on the polypeptide produced and hence phenotype shown?

A

1) Silent mutation -where the new codon May code for the same amino acid so there is no change to the polypeptide.
2) an amino acid wifh a similar chemical nature may be substituted and :: the effect is small e.g If valine replaces glycine.
3) a mutation at a significant site in the protein molecule will make a significant difference to the activity of the protein e.g if the protein were an enzyme the active site may be destroyed.

101
Q

Why are bacteria frequently used in experiments studying mutations?

A

Because they have a short life cycle and high rate of mutation

102
Q

What causes sickle cell anaemia?

A

A substitution point mutation in the gene producing the beta polypeptide of haemoglobin.

103
Q

Describe how sickle cell anaemia occurs in detail.

A

A DNA triplet on the coding strand, CTC, codes for the amino acid glutamate. Substituting A for T, at the second position, produces the triplet see a CAC,which codes for valine. The side chain of the glutamate is large and hydrophilic where is that availing is small and hydrophobic. When the oxygen tension is low. The affected haemoglobin within the red blood cell aggregates. The cell membrane collapses on the precipitated haemoglobin and the red blood cell becomes sickle shaped.

104
Q

What are the consequences of sickle cell anaemia to the structure of the cell?

A

The red blood cells of a person become fragile and may break in the capillaries.

105
Q

What is DNA polymerases error rate compared to RNA polymerases?

A

DNA polymerase= 10 to the power of 10

RNA polymerase= 10 to the power of 5

106
Q

What are some side effects of sickle cell anaemia?

A

1) ability of red blood cell to carry oxygen is reduced leading to anaemia.
2) possible death
3) joint pain
4) organ damage

107
Q

The alleles for producing normal haemoglobin Hb(A) and mutant haemoglobin Hb(S) are co-dominant, what does this mean?

A

This means that heterozygous individuals Hb(A)Hb(S) have sickle cell traits where at least 50% of their haemoglobin is Hb(A) (normal) and show less severe symptoms.

108
Q

What are chromosome mutations?

A

Changes in the structure or number of chromosomes in cells.

109
Q

When do mutations affecting a chromosomes structure occur?

A

During prophase I of meiosis, homologous chromosomes pair and exchange material at the chiasmata.
If the chromosomes don’t rejoin accurately at the corresponding position on its homologous partner mutations occur.

The homologous chromosomes (hence gametes), end up with some different genes. 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.

110
Q

When are changes in the number of chromosomes likely to occur?

A

During meiosis when homologous chromosomes separate at anaphase I, it when chromatids separate at anaphase II.

111
Q

Define the term non-disjunction

A

A faulty cell division in meiosis following which one of the daughter cells receives two copiers of a chromosome and the other receives none.

112
Q

What happens in Down’s syndrome.

A

It is a form of non-disjunction where one secondary occyte has either no chromosome 21 or two copies of the chromosome 21.
Those with no chromosome 21 can’t produce a viable embryo.
Those with 2 copies of embryo 21 fuse with normal sperm to produce a viable embryo with cells containing 3 copies of chromosome 21, with a total of 47 chromosomes.
This condition is called trisomy 21 and produces Down’s syndrome.’

113
Q

What happens in translocation Downs

A

A fragment of one chromosome attaches to another.
During meiosis in a gamete that produced them, a fragment of chromosome 21 attaches itself to chromosome 14. When that abnormal gamete fuses with a normal one, it produces an embryo with 2 normal copies of chromosome 21 and an additional one attached to chromosome 14.

114
Q

Define the term polyploidy

A

Having more than 2 complete sets of chromosomes.

115
Q

What are cells with complete sets of chromosomes described as?

A

Euploid

116
Q

What are cells with a small number of extra chromosomes or a small number too few (as a result of non-disjunction) called?

A

Aneuploid.

117
Q

How may polyploidy arise?

A

1) if two diploid gametes fuse, a tetraploid (4n) is produced
2) endomitosis where the replication of chromosomes is not followed by cytokinesis.

3)a defect in the spindle at meiosis May result in all of the chromosomes at anaphase I, or all of the chromatids at anaphase II moving to the same pole, making gametes with 2 of each chromosome.
When a diploid gamete is fertilised by a normal haploid gamete a Triploid zygote with 3 sets of chromosomes is formed.

118
Q

What organisms is polyploidy common in?

A

Flowering plants

119
Q

What beneficial characteristics is polyploidy associated with?

A

Vigour and disease resistance as seen in 4n potatoes and 6n bread.

120
Q

Why is polyploidy much more common in plants than in animals?

A

Because plants:

  • reproduce asexually
  • are hermaphrodite and so do not use chromosomes to determine their sex.
121
Q

Name 2 animals which have polyploid chromosomes

A

Salmon as goldfish

122
Q

What is a carcinogen?

A

An agent that causes cancer

123
Q

Define the term oncogene

A

A proto-oncogene with a mutation that results in cancer.

124
Q

What controls cells division?

A

Genes

125
Q

When is cell division halted?

A

When enough cells have been produced for growth and repair

126
Q

What are tumour suppressor genes?

A

Genes that regulate mitosis and prevent cells dividing too quickly

127
Q

What would a mutation in a tumour suppressing gene cause?

A

It would loose regulatory function and :: the cell could go into continual repeated mitosis which characterises cancer.

If the cell escapes attack from the immune system it produced a collection of cells called tumour cells.

128
Q

What is a malignant tumour?

A

Tumours which spread spread around the body and invade other tissues making secondary tumours or metastases.

129
Q

Which gene with abnormalities codes for a protein that has been found in over half of all cancers?
What protein is this?

A

Abnormalities in the TP53 gene.

It codes for the p53 protein which has been identified in more than half of all cancers.

130
Q

How does mutant p53 gene contribute to the development and spread of cancer?

A

1) no DNA repair (normal p53 activates repair of damaged DNA)
2) cell with damaged DNA enters S phase and DNA is replicated (normal p53 prevents the cell from entering the S phase, holding it in G1 while damaged DNA is repaired)
3) mutant cells survive and undergo mitosis (normal p53 initiates apoptosis if damaged DNA can’t be repaired)

131
Q

When do proto-oncogenes cause cancer?

When do tumour suppressor genes cause cancer?

A

Proto-oncogenes cause cancer when they are permanently switched on.

Tumour suppressor genes cause cancer when they are switched off.

132
Q

What happens if a proto-oncogene is mutated so it’s switched on?

A

Excessive amounts of the protein are made, causing rapid repeated mitosis I.e cancer.

133
Q

What is a proof-oncogene called if it’s mutated so that it causes cancer?

A

Oncogene

134
Q

What causes prior-oncogenes to become oncogenes?

A

1) a mutation which causes chromosomes to rearrange, and places the proto-oncogene next to a DNA sequence that permanently activated it
2) there is an extra copy of the proto-oncogene resulting in too much of its product being made, causing excessive mitosis.

135
Q

What does tobacco smoke contain?

A

Contains over 4000 chemicals, including tar, nicotine and carbon monoxide.
40 of which are known to be carcinogenic and over 400 others known to be toxic.

136
Q

Explain why tobacco smoke is carcinogenic.

A

Tar collects in the lungs and tobacco smoke cools it.

Some polycyclic hydrocarbons can enter the nuclei of alveolar cells and slide between the base pairs in the DNA causing mutation by preventing accurate replication.

137
Q

What is epigenetics?

A

The control of gene expression by modifying DNA or histones, but not by affecting the DNA nucleotide sequence.

138
Q

What are the 3 causes for variation between members of a species?

A

1) differences in DNA nucleotide sequence i.e different alleles
2) physiological effects of the environment e.g higher light intensity increasing plant growth
3) epigenetic changes where the environment alters the expression of genes by affecting how they are transcribed without changing their nucleotide sequence.

139
Q

Describe the effects of DNA methylation as an epigenetic change

A

Cytosine can have a methyl or hydroxymethyl group added, and :: methylated cytosine can be read as cytosine pairing with guanine are transcription.

But if regions are too heavily methylated they are less likely to be transcribed.

140
Q

What is a Histone modification?

A

It’s a modification it histone following translation by attaching an Acetyl group to the amino acid lysine, a methyl group to lysine and arginine or a phosphate group to define and threonine.

141
Q

Describe the effects of the modification of histone as an epigenetic change.

A

Changes to histone proteins alter its interaction with DNA by changing the arrangement with nucleosomes.

When Unmodified the nucleosomes pack more tightly :: the DNA is less accessible to enzymes and so transcription is reduced.

When histones are modified the coiling is more relaxed and transcription factors and RNA polymerase have access to the DNA so transcription is increased.

142
Q

What is evidence for epigenetic changes in real life?

A

Monozygotic twins provide evidence: they have identical nucleotide sequences as they come from the same fertilised oocyte.
Their DNA methylation and histone acetylation is very similar initially but the difference between them increase as they get older and they increase the longer twins are apart.

143
Q

Name 2 consequences of epigenetic changes

A

1) Genomic imprinting -a gene may be permanently switched off by DNA methylation on the chromosome derived from one parent leading to a medical condition in the next generation.
2) X inactivation -epigenetic changes can switch off a whole chromosome e.g cells of female mammals only using one X chromosome.

144
Q

Give an example of genomic imprinting

A

Only the fathers copy of the NOEY2 gene is expressed normally, however if like the mothers it is not (due to inactivation) the risk of breast/ovarian cancer is increased.

145
Q

Give an example of X inactivation

A

The patchwork of tortoiseshell cats reflects the random inactivation of one of the mothers X chromosomes, and :: the fur colour gene they carry.

146
Q

What conditions have epigentic changes been linked to (general)

A

Autoimmune conditions
Mental illness
Diabetes
Many cancers

147
Q

What will the studies of epigenetics be useful for in the future?

A

Very important in disease detection, treatment and prevention.

Biology Unit 4 (3 decks)

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