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A level Biology > 6.2 Patterns of inheritance > Flashcards

6.2 Patterns of inheritance Flashcards

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1
Q

define genotype

A

Genetic makeup of an organism

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2
Q

define phenotype

A

visible characteristic of an organism

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3
Q

define mutagen

A

agents which increase the rate of mutation

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4
Q

What are the three types of mutagens

A

physical agents
chemical agents
biological agents

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5
Q

Give examples of chemical mutagens

A

mustard gas
nitrous acid
aromatic amines

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6
Q

Give examples of physical mutagens

A

X-rays
gamma rays
UV light

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7
Q

Give examples of biological mutagens

A

viruses
food contaminants

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8
Q

What is a persistent mutation

A

can be transmitted through many generations without change

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9
Q

What is a random mutation

A

they are not directed by a need on the part of the organism in which they occur

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10
Q

What are the 5 types of chromosome mutations

A

deletion
inversion
translocation
duplication
non-disjunction

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11
Q

Describe deletion chromosomal mutation

A

part of a chromosome containing genes and regulatory sequences is lost

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12
Q

Describe inversion chromosomal mutations

A

A section of chromosome may break off, turn 180 degrees then join again

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13
Q

Why are inversion mutations harmful

A

although all the genes are still present some may now be too far away from their regulatory nucleotide sequences to be properly expressed

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14
Q

Describe translocation chromosomal mutations

A

a piece of one chromosome breaks off and then becomes attached to another chromosome

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15
Q

Describe duplication chromosomal mutations

A

a piece of chromosome may be duplicated and overexpression of genes may be harmful

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16
Q

Describe non-disjunction chromosomal mutations

A

one pair of chromosomes or chromatids fails to separate leaving one gamete with an extra chromosome.
When fertilized by a normal haploid gamete the resulting zygote has one extra chromosome

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17
Q

Define aneuploidy

A

the chromosome number is not an exact multiple of the haploid number as chromosomes or chromatids may fail to separate during meiosis - trisomy

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18
Q

Define polyploidy

A

if a diploid gamete is fertilised by a haploid gamete the resulting gamete the zygote will be triploid - have 3 sets of chromosomes

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19
Q

How dos sexual reproduction contribute to evolution

A

Genetic variation causes by random fusion of gametes, independent assortment of chromosomes during metaphase 1+2 and allele shuffling during prophase 1

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20
Q

Give examples of variation caused by environmental factors

A

speaking with an accent
scars
tattoos

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21
Q

Give examples of variation caused by genetic factors

A

eye colour
blood group

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22
Q

Give examples of variation caused by both environmental and genetic factors

A

skin colour
weight
height

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23
Q

Define heterozygous

A

having different alleles at a particular gene locus on a pair of homologous chromosomes

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24
Q

Define homozygous

A

True-breeding
having identical alleles at a particular gene locus on a pair of homologous chromosomes

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25
Q

define monogenic

A

determined by a single gene

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26
Q

define sex-linked

A

gene present on one of the sex chromosomes

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27
Q

define autosome

A

the pairs are fully homologous - they match in length and contain the same genes at the same loci

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28
Q

why are the sex chromosomes slightly homologous

A

so that they can pair up during meiosis

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29
Q

How is XX different to XY in terms of alleles

A

If a female has one abnormal allele on one of her X chromosomes she will probably have a functional allele on the other X chromosome
Whereas f a male inherits the abnormal allele on the X chromosome he will suffer from a genetic disease

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30
Q

Define codominance

A

where both alleles present in the genotype of a heterozygous individual contribute to the phenotype of an organism

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31
Q

Give an example of codominance

A

Red and white cows, when they mate can produce roan offspring

Humans can have AB blood types

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32
Q

Give examples of sex linkage

A

Males suffer from haemophilia A whereas females dont
Theyre are only female tortoise shell cats

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33
Q

Define multiple alleles

A

characteristic for which there are three or more alleles in the populations gene pool

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34
Q

give an example of a characteristic with multiple alleles

A

blood group

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35
Q

define autosomal linkage

A

gene loci present on the same autosome that are often inherited together

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36
Q

what is the mendeleian ratio for monohybrid inheritance

A

3:1

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37
Q

What are recombinant genes

A

when there is crossing over between two non-sister chromatids during prophase 1

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38
Q

What increases the chance of recombinant genes

A

the further the 2 gene loci are away from each other

39
Q

describe inheritance of autosomally linked genes with no crossing over

A

they are always inherited as one unit

40
Q

define dihybrid

A

involving two gene loci

41
Q

what is the ratio in a dihybrid cross

A

9:3:3:1

42
Q

When in autosomal linkage may there be more than the expected phenotypes

A

because the genes had crossed over

43
Q

what can we deduce from dihybrid crosses

A

The alleles of two genes are inherited independently of each other so each gamete has one allele for each gene locus

during fertilisation any one of an allele pair can combine with any one of another allele pair

44
Q

How does epistasis differ from dihybrid crosses

A

although 2 gene loci are involved with epistasis there is only 1 phenotype expressed

45
Q

Define epistasis

A

interaction of non-lined gene loci where one masks the expression of the other

46
Q

What are some examples of genes working antagonistically

A

recessive and dominant epistasis

47
Q

Define recessive epistasis

A

the homozygous presence of a recessive allele at the first locus prevents the expression of the other

48
Q

what are the second gene loci called in epistasis

A

they are said to be hypostatic to those at the first locus

49
Q

What is the ratio of recessive epistasis

A

9:3:4

50
Q

Define dominant epistasis

A

The presence of a dominant allele at the first locus prevents the expression of another allele at the second gene loci

51
Q

Give an example of recessive epistasis

A

inheritance of flower colour in salvia

52
Q

What is the ratio for dominant epistasis

A

12:3:1
13:3

53
Q

Give examples of dominant epistasis

A

feather colour in chicken

54
Q

why might there be a ratio of 13:3 in dominant epistasis

A

when the first dominant allele may prevent colour from being present in chicken
but in the second gene some alleles also may prevent colour being deposited as well

basically only two phenotypes able to be expressed white or coloured

55
Q

How may genes work in a complimentary fashion?

A

epistasis
genes working to code for two enzymes that work in succession catalysing sequential steps for a metabolic pathway

56
Q

Give an example of genes working in a complimentary action

A

coat colour in mice
allele C present means the mice will have a black coat and not albino
paired with allele A will create an agouti pattern

57
Q

What are the ratios for complimentary gene action

A

9:7 - 2 phenotypes available for expression
9:3:4
9:3:3:1

58
Q

What is the null hypothesis for the chi squared test

A

there is no statistically significant difference between the observed and expected data any difference is due to chance

59
Q

Define discontinuous variation

A

where phenotype classes are distinct and discrete and discernible from eachother in a qualitative way

monogenic or epistasis involved

60
Q

Give an example of discontinuous variation

A

blood group gender

61
Q

Describe continuous variation

A

Where genetic variation shows a range with a smooth gradation between intermediates
polygenic

62
Q

What are some examples of continuous variation

A

skin colour
height
tail length

63
Q

Which variation is able to be influenced by the environment

A

continuous

64
Q

Why might a 2:1 ratio be observed if 3:1 was expected

A

A pair of alleles may be lethal such as DD

65
Q

Why can some alleles be said to be codominant

A

both alleles are expressed in the phenotype and neither is dominant or recessive to each other

66
Q

By observing a graph how would you know that 2 genes are autosomally linked

A

the homozygous AB or ab are mostly produced from a heterozygous AaBb plant so for the alleles to be inherited together like this the 2 alleles must be on the same autosome

67
Q

What is a phenotypic trait of a plant that is determined by plants

A

chlorosis
lack of magnesium in soil

68
Q

Define speciation

A

the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation leading to the evolution of two or more new species

69
Q

Define allopatric speciation

A

formation of two different species from one original species due to geographical isolation

70
Q

Define sympatric speciation

A

formation of two different species from one original species due to reproductive isolation while the populations inhabit the same geographical location

71
Q

What are the different isolating mechanisms

A

geography
reproduction

72
Q

Describe geographical isolation

A

populations separated by geographical features such as lakes experience different selective pressures and undergo independent allele changes and each population becomes adapted to its environment

73
Q

describe reproductive isolation

A

biological or behavioural changes such as changes in time of activity or change in chromosome number or genitalia lead to speciation from reproductive isolation

74
Q

How can change in the number of chromosomes lead to reproductive isolation

A

prevents gamete fusion
zygote is less viable
infertile hybrid offspring

75
Q

Give example of evolution in action

A

tolerance to heavy metals in plants
antibiotic resistance

76
Q

define stabilising selection

A

normally occurs when the organisms’ environment remains unchanged and the intermediate phenotype is favoured
eg babies with a birth mass closer to 3.5 are more likely to survive

77
Q

define disruptive selection

A

where both of the extreme phenotypes are favoured and the intermediate is selected against

78
Q

define directional selection

A

if the environment changes there will be a gradual shift over generations of the optimum value of a trait

79
Q

when does genetic drift arise

A

after a genetic bottleneck or as a result of the founder effect

80
Q

Define genetic bottleneck

A

when population size shrinks then increases again eg after a catastrophic event

81
Q

What occurs after a genetic bottleneck

A

genetic diversity within the population will be reduced
loss of advantageous alleles or disproportionate frequency of harmful alleles putting the populations long term survival at risk

82
Q

When might a genetic bottleneck be advantageous

A

if ones that survive have a particular advantage for example resistance to a particular pathogen it may improve the gene pool while also shrinking genetic diversity

83
Q

Define the founder effect

A

if a new population is established by a very small number of individuals who originate from a larger population the new population is likely to experience loss of genetic diversity

84
Q

Why might populations that are a result of the founder effect exhibit a loss of genetic diversity

A

The migrating populations will not be genetically representative of he parent population and so will have a small gene pool

85
Q

What does the Hardy-Weinberg principle assume

A

population is large enough to make the sampling error negligible
mating occurs at random
there is no selective advantage for any genotype
no mutation, migration or genetic drift

86
Q

What 2 equations are used in the Hardy-Weinberg principle

A

p+q=1
P2+pq+Q2=1
where p=dominant
q=recessive

87
Q

What is the probability of gametes having two recessive or dominant alleles

A

p2
or
q2

88
Q

What is the probability of gametes having heterozygous alleles

A

2pq

89
Q

Define artificial selection

A

selective breeding of organisms where humans are the agents of selection by choosing the desired phenotype and interbreeding phenotypes individually

90
Q

define inbreeding depression

A

when related individuals are crossed and the chances of inheriting two copies of a harmful recessive allele are increased

91
Q

Define hybrid vigour

A

outcrossing individuals belonging to two different varieties to obtain individuals that are heterozygous at many gene loci

92
Q

What is the problem associated with artificial selection i plants

A

Reduces the organisms genetic diversity so they are more likely to succumb to the same pathogen
e.g. if temperatures rise above 30C when wheat crops are flowering then their metabolism is disrupted and seeds do not form

93
Q

What are some ethical considerations of artificial selection

A

domesticated animals may be less likely to be able to defend themselves and make them easy prey
lean animals may succumb in winter
desired traits in dogs may be disadvantageous in the wild

A level Biology (25 decks)

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