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A2 BIOLOGY > 4.3 inheritance > Flashcards

4.3 inheritance Flashcards

1
Q

what is an allele

A

a different form of a gene

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2
Q

homozygous

A

when two of the same alleles make up the genotype

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3
Q

heterozygous

A

when two different alleles make up the genotype

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3
Q

genotype

A

the genetic make up (ie. your alleles)

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4
Q

chromosome

A

genes and DNA are packaged into these in the nucleus of the cell

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5
Q

dominant

A

one allele is needed for the phenotype to be shown

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5
Q

recessive

A

both alleles are needed for the phenotype to be displayed

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6
Q

locus

A

position of a gene in a chromosome

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7
Q

F1 and F2

A

first and second generation

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8
Q

autosome

A

what the first 22 chromosomes are called

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9
Q

what is Mendel’s law of segregation

A

the characteristics of an organism are determined by factors (alleles) which occur in pairs. only one of a pair of factors (alleles) can be present in a single gamete

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10
Q

what is the law of segregation controlled by
(characteristics of an organism)

A
  • by single genes
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11
Q

what are characteristics an example of

A

discontinuous variation

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12
Q

what is discontinuous variation

A

things that won’t change (skin colour, blood type)

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13
Q

how to write a punnet square

A
  1. suitable symbol for alleles
  2. parents genotype
    3, gametes by each parent labelled and circled
  3. use punnet square to show results
  4. Label F1 (F2 if necessary)
  5. indicate the ratio of the phenotype
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14
Q

what is a test cross used for

A

to determine whether an organism showing the dominant characteristics of a trait is homozygous

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15
Q

what does a test cross involve

A

crossing the organism with another that is homozygous recessive for the trait

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16
Q

what would show the parents must have been heterozygous in the test cross

A

if any of the offspring show the homozygous recessive trait in the phenotype, parent must have been heterozygous

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17
Q

what is co dominance

A

both alleles show up in the phenotype equally

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18
Q

what is incomplete dominance

A

-where the phenotype of the heterozygote is intermediate between the two parental phenotypes

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18
Q

what is mendels second law of inheritance called

A

the law of independent assortment

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19
Q

what is the law of independent assortment

A

‘each member of an allelic pair may combine randomly with either of another pair’
where there is variation due to independent assortment and crossing over (during meiosis)

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20
Q

what does the law of independent assortment apply to

A

dihybrid inheritance

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21
Q

independent assortment (meiosis)

A

homologous chromosomes line up at the equator randomly so equal chances of chromosomes going to either pole
each gene behave independently of each other so are unlinked

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22
Q

why did mendel use peas in his experiments

A
  • easy to grow
  • characteristics controlled by single gene
  • characteristics controlled by genes on different chromosomes
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23
Q

what did mendels experiment conclude

A
  • round seed shape was dominant and wrinkled was recessive
  • yellow seed colour was dominant and green seed colour was recessive
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24
Q

what is dihybrid inheritance

A

the inheritance of two separate genes (that are unlinked)

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25
Q

when is inheritance down to linkage

A

when either medelian’s ratio’s are not shown

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26
Q

explain linkage

A

genes are on opposite chromosomes which segregate to oposite poles during meiosis
genes which are linked are on the same chromosome so cannot segregate during meiosis.

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27
Q

what can the chi-squared test be used for

A

to prove or disprove a null hypothesis

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28
Q

what is a null hypothesis

A

states that any deviation between observed and expected is due to chance (no significant difference)

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29
Q

when does the chi-squared test accept or reject

A

accept- no significant difference
reject - there is significant difference

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30
Q

what is a hermaphrodite
and examples

A

organism that has reproductive organs of both sexes
most angiosperms are hermaphrodite
also invertebrate hermaphrodites e.g. Mollusca and Annelida

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31
Q

what can hermaphrodites do

A

self-pollinate

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32
Q

other reproductive strategies

A

-monoceious plants
-dioecious plants

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33
Q

what is a dioecious plant

A

some plants are male other are female
e.g holly, willow, cannabit

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33
Q

what is a monocious plant

A

male and female om the same plant
e.g Maize

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34
Q

most vertebrates have separate males and females but what can the ratios be controlled by

A

Temperature
Sequential hermpahroditism
hierarchy
hermaphrodite (during deperate times)
ploidy level
chromosomes structure (humans)

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35
Q

what implications could having a different pair of chromosomes have on inheritance

A

if they’re not identical, no homologous portion on the Y chromosome
recessive alleles on this non-homologous portion of the X chromosome will appear more frequently in the male. no portion with dominant allele

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36
Q

what is sex linkage

A

where the phenotypic expression of the allele that is dependent on the sex of the individual and is directly tied to the sex chromosome

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37
Q

why is x linkage more common

A

the X chromosome is larger
part of it doesn’t have a homologous section on the Y chromosome, so only one allele of a gene will be present and will always be expressed

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38
Q

what part of the gene carry sex determining genes

A

non-homologous regions

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39
Q

examples of X- linked diseases

A

Haemophilia
Duchenne muscular dystrophy
red green colour blindness

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40
Q

what genes are described as sex linked

A

genes that are located on the sex chromosomes

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41
Q

what does the study of sex linked genes involved

A

examining both the sex of the offspring and the genetic trait of interest

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42
Q

Y linked diseases

A

are rare and debateable
it is argued that there is little room on the Y chromosome for anything other than genes controlling the testes formation and function

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43
Q

what is haemophillia

A

x-linked disease where blood clots slowly leading to internal bleeding (lethal if not treated)

44
Q

explain the development of haemophilia

A

recessive allele with altered DNA nucleotides, they do not code for required protein for blood clotting
Only linked to X chromosomes (none on Y)

45
Q

treatment for haemophiliacs

A

protein can be extracted from donated blood and given to them

46
Q

explain why males always inherit haemophilia from their mother (3 marks)

A
  • males can only obtain Y chromosome from father
    -males X chromosome must come from mother
    -allele that doesn’t code for clotting protein is linked to X chromosome
47
Q

explain colour blindness

A

allele for colour vision carried on X chromosome, males will only have one allele for colour vision
there is a defective, recessive allele of the colour vision gene that can lead to colour blindness (especially red or green)

48
Q

what is duchenne muscular dystrophy

A

duchenne is the most common and severe form of MD- about 100 boys are born with it each year
X-linked recessive allele of dystrophin gene

Dystrophin is a component of a glycoprotein stabilising cell membrane of muscle fibres
leading to a loss of muscle mass and weakness

49
Q

what is a mutation

A

a change in the amount, arrangement or structure of the DNA in an organism, they are random

50
Q

2 types of mutations

A

gene mutations e.g sickle cell
chromosome mutation
e.g downs

51
Q

what does a mutagen do

A

increase the chance of mutation

52
Q

examples of mutagens

A

ionising radiation
x rays
polucyclic hydrocarbons in cigarette smoke
chemicals e.g benzene

53
Q

when is a mutation expressed in
haploid / diploid organisms

A

haploid= mutation is expressed
diploid= mutations only expressed if dominant but this is rare or on the X-chromosome

54
Q

different ways which mutations can occur

A

gene or point mutation
chromosome mutation
aneuploidy
polypoidy

55
Q

explain gene or point mutation

A

changes in base sequence occurs if DNA is not copied correctly in S phase before cell division, this can lead to a different amino acid being added so a different protein is then translated

56
Q

what is duplication

A

the same gene twice

57
Q

what is inversion

A

where DNA bases exchange positions

58
Q

what are the effects of mutation
(silent)

A

changes in base doesn’t change the amino acid it codes for. mutation does not have a significant effect on the phenotype,
it might also be in an intron
or could be amino acid with similar chemical nature so won’t be of much effect

59
Q

what happens if a mutation is on an active site of enzyme

A

it would have a significant effect

60
Q

what is Duchenne muscular dystrophy

A

the most common and severe form of MD, about 100 boys are born with it each year, includes a loss of muscle mass and progressive muscle weakness

61
Q

what is DMD caused by

A

a sex linked recessive allele of a gene that codes for the protein dystrophin, dystrophin is a component of a glycoprotein that stabilises the cell membranes of muscle fibres

62
Q

when are sex linked recessive alleles expressed

A

only expressed in females if both X chromosomes carry the allele
are always expressed in the male because the Y chromosome does not have a homologous locus for the gene

63
Q

what is sickle cell an example of

A

point mutation

64
Q

explain how sickle cell anaemia is caused

A

by a single mutation in the gene coding for haemoglobin
HBB gene is on chromosome 2
this mutation involves a substitution of A for a T (valine instead of glutanic acid)
this changes 1 amino acid (changes properties)

65
Q

what happens to people with sickle cell anaemia when oxygen levels are too low

A

red cells deform and block capillaries

66
Q

what does the HbSHbS allele do

A

reduces the ability of RBC to carry oxygen which can lead to death

67
Q

what is an example of a chromosome mutation

A

down syndrome (Trisomy 21)

68
Q

how common is downsyndrome

A

1/800 births

69
Q

what is downsyndrome a consequence of

A

non-disjunction in humans

70
Q

what is non-disjunction (in downsyndrome)

A
  • where chromosomes fail to separate at anaphase 1 of meiosis
    occurs for chromosome 21 resulting in a gamete containing an extra chromosome 21, this is then fertilised by a normal gamete
    (47 gametes)
71
Q

what happens if non-disjuntion occurs on a different chromosomes

A

will normally result in miscarriages of the foetus

72
Q

why can the offspring survive with a chromosomal mutation (down syndrome)

A

because the 21st chromosome is relatively small carrying only around 200 to 300 genes out of an estimated total of 20000-25000 for the human genome so the offspring can survive

73
Q

what is translocation downs

A

still have 46 chromosomes
fragments of chromosome 21 attaches to chromosome 14

74
Q

what are mutations a source of

A

genetic variation which can result in evolution through natural selection

75
Q

when do most mutations occur

A

during crossing over during prophase-1 of meiosis or as a result of non-disjunction during anaphase-1 or anaphase-II of meiosis

76
Q

what are ploidy levels

A

changes in numbers of sets of chromosomes

77
Q

explain endomitosis

A

division of chromosomes not followed by nuclear division that results in an increased number of chromosomes in the cell

78
Q

what can mutations affect

A

protein synthesis and can change the phenotype of an organism, but some mutations have no effect on the phenotypes

79
Q

what do gene/point mutations affect

A

a single base in a gene and chromosomal mutations affect many genes

80
Q

what is a mutagen that causes cancer called

A

carcinogen

81
Q

what can happen to protein-oncogenes

A

they can mutate to become oncogenes which are involved causing uncontrolled cell division to form a cancer

82
Q

what is the role of the tumour suppressor gene

A

regulate cell division

83
Q

what happens if a mutation affects a tumour suppressor gene

A

then cell division is no longer controlled

84
Q

how is a tumour formed

A

if the mass of cells (from the tumour suppressor genes being mutated) isn’t detected and destroyed by the immune system then it will continue to divide

85
Q

when do tumour suppressor genes cause cancer

A

when it’s turned off

86
Q

what is a proto-oncogene

A

a gene that helps to control cell division, codes for a protein that contributes to cell division

87
Q

when do proto-oncogenes cause cancer

A

when turned on

88
Q

what is an oncogene

A

a mutated protein-oncogene

89
Q

what is epigenetics

A

the study of changes to DNA after DNA replication

90
Q

what is gene expression controlled by

A

factors other than the DNA sequence

91
Q

what are variation in organisms usually caused by

A
  • different alleles (a difference in nucleotide sequence)
  • environmental evidence
92
Q

what can also bring about epigenetic changes

A

the environment

93
Q

what does DNA being modified post-replication mean

A

doesn’t change the DNA base sequence but changes the ability of a gene to be transcribed during protein synthesis

94
Q

what can epigenetic changes be influenced by

A

-age
-environment
-lifestyle
-drugs
-during growth in pregnancy or childhood

95
Q

what are the 2 ways to affect the transcription of genes without changing the nucleotide sequence

A

-methylation of cytosine
-histone modification

96
Q

what is methylation of cytosine

A

-cytosine can have a methyl group added to it, it can still pair with Guanine but regions heavily methylated cannot transcribe DNA as well

97
Q

what does the addition of methyl groups to bases do

A

reduces the ability of that gene being expressed

98
Q

what is gene expression

A

is the process by which information from a gene is used in the synthesis of a functional product e.g. proteins or functional RNA

99
Q

what is histone modification

A

DNA is coiled around proteins called histones
histones can be modified epigenetically and these changes alter interaction with DNA to make it more or less densely coiled

100
Q

what does it mean when the histone coils more tightly

A

they can prevent gene expression

101
Q

what does it mean when the histone coiled loosely

A

they can increase gene expression

102
Q

where can different epigenetic modification occur

A

in cells of the same tissue and in different tissues resulting in different expression of the same gene in different parts of the same organism

103
Q

explain what X-inactivation is

A

epigenetic changes can switch off a whole organism e.g. in females only 1x chromosome is used, the other is inactivated

104
Q

an example of X-inactivation

A

fur colour is on the X chromosome and the alternate chromosomes are switched off in different groups of cells

105
Q

what is a stem cell

A

an undifferentiated human cell that are able to undergo mitosis to develop to many specialised things

106
Q

explain how DNA methylation can result in tumour growth

A

mRNA from regulator is not produced so regulator protein isn’t produced. suppressor gene is not expressed/switched on. so uncontrolled mitosis

107
Q

if tumour suppressor genes are permanently switched off what would the consequences be

A

increased risk of cancer
passed on to next generation

108
Q

what is polyploidy

A

some organisms have additional complete sets of chromosomes (e.g three sets of chromosomes=triploid 3n)

109
Q

what does meiosis do

A

brings about variation in offspring produced by sexual reproduction

110
Q

three ways meiosis brings about variety

A

-2 haploid gametes must fuse during feretilisation, each contains half the genetic information of the parent resulting in a unique new combination of genetic info
- random distribution and independent assortment of homologous chromosomes (random)
- crossing over during chiasmata formation during prophase I of meiosis, new genetic combinations and the separation of linked genes

111
Q

why is variation so important

A

ensures some will have characteristics that allow survival even if the environment changes-

112
Q

why is crossing over so important

A

if it occurs between two genes, this separates alleles that were previously linked and allows them to combine in new recombiant genotypes (important source of variation)

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