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OCR AS/A Level Biology Context > module 6.1.2: patterns of inheritance > Flashcards

module 6.1.2: patterns of inheritance Flashcards

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1
Q

what are the 2 types of phenotypic variation

A

discontinuous and continuous

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2
Q

what is discontinuous variation

A

genetic variation producing discrete (discontinuous) phenotypes, so two or more non-overlapping categories
- traits tend to be monogenic, so different alleles have very different effects on the phenotype.
- can be represented using a bar charts unaffected by the environment

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3
Q

what is continuous variation

A

genetic variation that produces phenotypic variation where quantitative traits vary by very small amounts between one group and the next
- characteristics tend to be polygenic

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4
Q

the greater the number of gene loci…..

A

the more continuous the variation

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5
Q

how can the continuous variation data be represented

A

represented on a histogram

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6
Q

what is continuous variation influenced by

A

the environment
- eg. if plants are kept in dim light after germination, or if the soil contains insufficient magnesium, then the leaves of the plant do not develop enough chlorophyll and are yellow-white. the plant produced is chlorotic and unable to photosynthesise. it has the genotype for making chlorophyll, but environmental factors have prevented the expression of these genes

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7
Q

what is the main role of meiosis

A

the production of haploid gametes as cells produced by meiosis have half the number of chromosomes

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8
Q

how is genetic variation achieved during meiosis

A

crossing over
independent assortment

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9
Q

what happens during crossing over and when does it happen

A

where pairs of homologous chromosomes line up and exchange some of their genetic material
prophase 1

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10
Q

what happens during the independent assortment of chromosomes and when does it happen

A

the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle

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11
Q

what is an allele

A

a version of a gene

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12
Q

what is a locus

A

the specific position of a gene on a chromosome, the two alleles of a gene are found at the same loci on the chromosome pairs

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13
Q

what is a phenotype

A

visible characteristics of an organism

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14
Q

what is genotype

A

genetic makeup of an organism

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15
Q

what is a dominant allele

A

only a single allele is required for the characteristic to be expressed, that allele is always expressed in the phenotype

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16
Q

what is a recessive allele

A

the characteristic is only expressed if there is no dominant allele present

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17
Q

what is homozygous

A

two identical alleles

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18
Q

what is heterozygous

A

two different alleles

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19
Q

what is codominance

A

both alleles contribute to the phenotype

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20
Q

how is closeness of two linked genes on a chromosome linked to the number of recombinant offspring

A

more closely linked genes means less separation and so less recombinant offspring

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21
Q

what is a karyotype

A

display of every pair of homologous chromosomes within a cell, organized according to size and shape

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22
Q

what is a phenotype

A

physical characteristics of an organism

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23
Q

types of factors that contribute to phenotypic variation

A

environmental
genetic

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24
Q

environmental factor that contributes to phenotypic variation in animals

A

diet

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25
Q

examples of phenotypic variations caused by environmental conditions in plants

A

etiolation
chlorosis

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26
Q

etiolation

A

when a plant has elongated stems and has a pale colour due to a lack of chlorophyll because of insufficient light in the environment

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27
Q

chlorosis

A

when the leaves look pale or yellow because the cells aren’t producing enough chlorophyll

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28
Q

environmental factors that lead to chlorosis

A

lack of light leading to chlorophyll production decreasing to conserve resources, mineral deficiencies of iron or magnesium, viral infections

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29
Q

how is genetic variation created within a species

A

sexual reproduction

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30
Q

how can sexual reproduction lead to genetic variation within a species

A

meiosis, random fusion of gametes at fertilisation

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31
Q

f1 generation

A

generation produced by mating dominant and recessive homozygous individuals, all offspring are heterozygous

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32
Q

f2 generation

A

the offspring of mating two heterozygous individuals

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33
Q

phenotypic ratio in an F2 generation in monogenic inheritance

A

3:1

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34
Q

codominance

A

when two equally dominant alleles occur for a gene as the genotype is heterozygotic so are both expressed in the phenotype

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35
Q

how is codominance represented

A

capitals with a letter index

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36
Q

phenotypic ratio in an F2 generation in codominance

A

1:2:1 (homozygous, heterozygous, homozygous)

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37
Q

multiple alleles

A

when a gene has more than two versions

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38
Q

example of a characteristic caused by multiple alleles

A

blood group

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39
Q

characteristics of the multiple alleles involved in determination of blood group

A

IA and IB are codominant, IO is recessive, IA and IB are dominant to IO

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40
Q

X linkage

A

when a person assigned male at birth only has one copy of gene on the X chromosome so conditions caused by recessive alleles are more common in people assigned male at birth

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41
Q

why is X linkage a thing

A

the Y chromosome is smaller than the X chromosome so there are fewer genes on it

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42
Q

how to represent X linkage

A

X to an index, Y

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43
Q

phenotypic ratio when a carrier female mates with a normal male and the characteristic is X linked

A

half of all AMABs will have disorder, half of AFAB will be carriers

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44
Q

phenotypic ratio for dihybrid inheritance

A

9:3:3:1

45
Q

why may an actual phenotypic ratio be different from the theoretical one

A

fertilisation is random so small sample can be skewed by a few chance events, genes being studied are both on the same chromosome in linkage

46
Q

linkage

A

genes are on the same chromosome

47
Q

how are linked genes inherited

A

as one unit, no independent assortment unless they are separated by chiasmata

48
Q

the closer genes are on a chromosome…

A

the less likely they are to be separated during crossing over

49
Q

why may a ratio for linkage not be the expected

A

crossing over

50
Q

equation for recombination frequency

A

Recombination frequency = Number of recombinant offspring/ Total number of offspring

51
Q

what does a recombination frequency of 50% indicate

A

no linkage

52
Q

what recombination frequency suggests linkage

A

less than 50%

53
Q

how to use recombination frequencies to map a chromosome

A

recombination frequency of 1% is 1 map unit on a chromosome

54
Q

epistasis

A

interaction of genes at different loci

55
Q

examples of gene epistasis

A

gene regulation

56
Q

hypostatic

A

gene that is affected by another gene

57
Q

epistatic

A

gene that affects the expression of another gene

58
Q

recessive epistasis

A

homozygous presence of a recessive allele prevents expression of another allele at a second locus

59
Q

phenotypic ratio for recessive epistasis

A

9:3:4

60
Q

dominant epistasis

A

presence of dominant allele at one gene locus masks the expression of alleles at a second locus

61
Q

phenotypic ratio for dominant epistasis

A

12:3:1

62
Q

complementary epistasis

A

homozygous recessive genotypes at either locus masks the expression of the dominant allele at the other locus

63
Q

phenotypic ratio for complementary epistasis

A

9:7

64
Q

role of chi squared test

A

to determine the significance of the difference between observed and expected results

65
Q

degrees of freedom for chi squared test

A

n-1

66
Q

factors that lead to continuous variation

A

polygenetic
environmental

67
Q

factors that lead to discontinuous variation

A

few genes

68
Q

allele frequency

A

relative frequency of a particular allele in a population

69
Q

gene pool

A

sum total of all the genes in a population at a given time

70
Q

letter that represents the frequency of a dominant allele in the Hardy-Weinberg equation

A

p

71
Q

letter that represents the frequency of a recessive allele in the Hardy-Weinberg equation

A

q

72
Q

equations for Hardy-Weinberg

A

p + q = 1, p^2 + 2pq + q^2 = 1

73
Q

Hardy-Weinberg Principle

A

in a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution

74
Q

assumptions for the Hardy-Weinberg Principle

A

no mutations, no migration, equal fertility of each phenotype, each phenotype is as preferable as each other, large population required

75
Q

p^2

A

frequency of homozygous dominant genotype in the population

76
Q

2pq

A

frequency of heterozygous genotype in the population

77
Q

q^2

A

frequency of homozygous recessive genotype in the population

78
Q

role of the Hardy-Weinberg Principle

A

to calculate allele frequencies in a population

79
Q

allele

A

version of a gene with a unique base sequence

80
Q

recessive

A

an allele that won’t be expressed in the phenotype if there are any dominant alleles present

81
Q

which type of variation has an additive effect

A

continuous

82
Q

factors that can affect the evolution of a species

A

stabilising selection, directional selection, genetic drift, genetic bottleneck, founder effect

83
Q

stabilising selection

A

when the mean value is selected for and the extreme values are selected against

84
Q

effect of stabilising selection on the normal distribution curve

A

gets narrower

85
Q

directional selection

A

when the organisms with extreme phenotypes are selected for as a result of a change in the environment

86
Q

example of directional selection

A

peppered moths in the industrial revolution

87
Q

genetic drift

A

changes in allele frequency due to the random nature of mutations

88
Q

which populations will genetic drift have a larger effect in

A

small populations

89
Q

why will genetic drift have a larger effect in small populations

A

smaller gene pool

90
Q

genetic bottleneck

A

large decrease in population size that lasts for at least one generation

91
Q

founder effect

A

when a new colony is established by a few individuals, leading to the creation of a small population

92
Q

what is the founder effect an example of

A

genetic drift

93
Q

types of speciation

A

allopatric
sympatric

94
Q

allopatric speciation

A

when some members of a population are separated from the larger population by a physical barrier and are geographically isolated, leading to the evolution of a new species

95
Q

how does allopatric speciation lead to the evolution of a new species

A

selection pressures different in different environments, different alleles considered advantageous, different alleles selected for

96
Q

example of allopatric speciation

A

Darwin’s finches

97
Q

sympatric speciation

A

when organisms are isolated by reproductive mechanisms but live in the same habitat, leading to the evolution of a new species

98
Q

examples of mechanisms of reproductive isolation

A

ecological isolation, behavioural isolation, mechanical isolation, gametic isolation, temporal isolation

99
Q

artificial selection

A

organisms with alleles that are advantageous to the breeder are selected for so its frequency increases

100
Q

example of selective breeding in plants

A

hybridising okra with hibiscus to confer resistance to yellow vein mosaic disease

101
Q

examples of selective breeding in animals

A

Belyaev’s Foxes, breeding of dachshunds for small size and short legs so they could follow prey into burrows (I don’t trust any dog whose stomach touches the floor)

102
Q

example of maintaining resources of genetic material

A

seed banks

103
Q

importance of maintaining resources of genetic material

A

used in selective breeding

104
Q

use of genetic resources from seed banks

A

outbreeding to reduce the occurrence of homozygous recessive conditions due to inbreeding

105
Q

ethical considerations surrounding the use of artificial selection

A

can lead to health problems and homozygous recessive conditions

106
Q

examples of health problems occurring as a result of the use of artificial selection

A

big dogs have hip and heart problems, skull of the King Charles spaniel is too small to accommodate the brain

107
Q

monogenic inheritance

A

when a phenotype or trait is controlled by a single gene
- eg. cystic fibrosis where the individuals with doubly recessive genotype are affected

108
Q

dihybrid cross

A

inheritance of two genes simultaneously. the two genes are inherited independently of each other and so each gamete has one allele for each of the two gene loci. this means that during fertilisation any one of an allele pair can combine with any one of another allele pair. the probability of any two traits being inherited together if they are not linked is the product of the individual probabilities

109
Q

autosomal linkage and when does it occur

A

genes which are located on the same chromosome (which is not a sex chromosome) and tend to be inherited together in the offspring. occurs as the chromosome, not the gene, is the unit of transmission during meiosis, so linked genes are very unlikely to be separated by independent assortment. if linked genes are not affected by crossing over of non-sister chromatids during prophase 1 then they are always inherited as one unit

OCR AS/A Level Biology Context (24 decks)

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