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Genetics > Exam 4 > Flashcards

Exam 4 Flashcards

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1
Q

qualitative trait

A

only a few distinct phenotypes

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2
Q

quantitative trait

A

continuously variable over some measure (distribution is due to polygenic, environment, multifactorial)

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3
Q

polygenic

A

many genes involved

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4
Q

environment

A

different genotypes perform differently based on their environment

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5
Q

multifactorial

A

traits that are both polygenic and influenced by environment

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6
Q

3^n

A

number of possible genotype combinations
(n=number of loci, 3=number of alleles)

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7
Q

why is there a distribution, a range of phenotypes?

A

there are a large number of genes that influence them to dictate the phenotype, there are multiple loci segregating

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8
Q

in a graph that shows three distributions (AA, Aa, aa), they overlap, why? what can we assume about the person’s genotype on a particular part of the graph?

A
  • we know the phenotype of the individual but no the genotype
  • one of the genotypes is more likely than the others, but all genotypes are possible
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9
Q

what is the most important binary trait?

A

alive or dead

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10
Q

threshold traits

A

need a certain number of a particular allele before you manifest the phenotype

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11
Q

Nilsson-Ehle’s Wheat Kernel Color

A

early determination of quantitative traits, found that the extremes resembled the parents

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12
Q

the difference between the inheritance of genes influencing quantitative vs qualitative characteristics is the _________ ___ ____ ____ _______ ___ __________

A

number of loci that determine a characteristic

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13
Q

the proportion of F2 individuals that resemble one of the original parents can be used to estimate the number of ________ affecting a polygenic traits

A

genes

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14
Q

1/4^n

A
  • n= the number of loci
  • gives you the offspring that look like the parents
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15
Q

“all models are wrong but some are useful”

A

stuff is complex, we cannot account for everything, so we simplify it

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16
Q

types of distributions

A
  • normal
  • bimodel
  • skewed
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17
Q

mean

A

provides information about the center of a distribution

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18
Q

variance

A

indicates the variability of a group of measurements, or how spread out the distribution is

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19
Q

range of variance

A

0 to positive infinity

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20
Q

standard deviation

A

square root of variance

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21
Q

what genotype would have the least amount of variance?

A

homogenous

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22
Q

covariance

A

how two measurements vary together

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23
Q

range of covariance

A

negative infinity to positive infinity

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24
Q

correlation

A

the strength of association between 2 measurements

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25
Q

range of correlation

A

ranges from negative 1 to positive 1

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26
Q

correlation does _____ equal causation

A

NOT

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27
Q

types of correlation

A
  • positive (upward slanted line)
  • negative (downward slanted line)
  • strong
  • weak
  • none (straight line)
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28
Q

regression

A

linear relationship between 2 variables (allows predictions to be made)

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29
Q

y=mx+b
y=bx+a

A
  • m/b = slope
  • b/a = intercept
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30
Q

heritability

A

the proportion of the total phenotypic variation that is due to genetic differences

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31
Q

phenotypic variance (Vp = )

A

Vp = VA + VD + VI + VE + VGE

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32
Q

genotypic variance (VG = )

A

VG = VA + VD + VI

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33
Q

VA

A
  • additive
  • comprises the additive effects of genes on the phenotype, which can be summed to determine the overall effect on the phenotype
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34
Q

VD

A
  • dominance
  • alleles at a locus are not additive; rather the affect of an allele depends on the identity of the other allele at that locus (TT and Tt have the same phenotype value and tt is different)
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35
Q

VI

A
  • interaction
  • epistatic effects where one locus “masks” the effect of others
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36
Q

VE

A
  • environment
  • differences that result from environmental factors
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37
Q

VGE

A
  • gene-by-environment
  • effect of a gene depends on specific environment in which it is found
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38
Q

what is environmental impact hardest on?

A

plants! They cannot move

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39
Q

types of heritability

A
  • broad sense of heritability
  • narrow sense of heritability
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40
Q

broad sense heritability: equation

A

H^2 = VG/Vp

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41
Q

narrow sense of heritability: equation

A

h^2 = VA/Vp

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42
Q

H^2

A

broad sense heritability, represents the proportion of phenotypic variance that is due to genetic variance

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43
Q

h^2

A

narrow sense heritability, represents the proportion of phenotypic variance that is due to additive genetic variance

44
Q

H^2 = 0

A

genetic varation does not contribute to the phenotypic variation in the trait. It is due to environmental factors.

45
Q

H^2 = 1

A

indicates that all of the phenotypic variance results from differences in phenotype

46
Q

H^2 = between 0-1

A

both genetic and environmental factors influence phenotypic variance

47
Q

________ variance is what is able to be reproductively selected for

A

additive

48
Q

calculating heritability

A
  1. eliminating one or more variance components
  2. comparing the resemblance of parents and offspring
  3. comparing the phenotypic variances of individuals with different degrees of relatedness
  4. measuring the response to selection
49
Q

phenotypic variance equation

A

Vp = VA + VD + VI + VE + VGE

50
Q

eliminating one or more variance components

A
    1. eliminate environmental variance (VE + VGE = 0)
    1. genetically identical individuals (VG = 0)
    1. raise clones or highly inbred, identically homogenous individuals in a defined environment and measure their phenotypic variance to estimate VE
51
Q

comparing the phenotypic variances of individuals with different degrees of relatedness raises a group of…

A

genetically variable individuals and measure phenotypic variance

52
Q

VG equation

A

Vp - VE

53
Q

when genetic differences are responsible for phenotypic variance, offspring should resemble their parents more than they resemble unrelated individuals, why?

A

offspring share 50% DNA with mom and 50% DNA with dad

54
Q

why are there deviations from the expected phenotypes?

A

due to mendelian sampling (meiosis, recombination, independent assortment)

55
Q

h^2 = b

A

regression of offspring mean against mean of both parents

56
Q

response to selection

A

the extent to which a characteristic subjected to selection changes in one generation

57
Q

selection differential

A

the difference between the mean phenotype of the selected parents and the mean phenotype of the original population

58
Q

limits to the response to selection

A
  • no genetic variability
  • biological limitations
59
Q

limitations to heritability

A
  • heritability says nothing about the degree to which genes determine a characteristic
  • no meaning for a specific individual (need a group)
  • specific to a given population in a given environment
  • high heritability does not mean environmental factors can’t influence the expression of a characteristic
  • cannot be used to draw conclusions about why populations differ in a characteristic
60
Q

what does high heritability indicate?

A

only that the environmental variation to which the population is CURRENTLY exposed to is not responsible for variation in the characteristic

61
Q

mendelian population

A

a group of interbreeding, sexually reproducing individuals that have a common set of genes

62
Q

population genetics

A

study the variation in alleles within and between groups and the evolutionary forces responsible for shaping the patterns of genetic variation found in nature

63
Q

genotype frequency = f(AA) =

A

number of AA individuals / N

64
Q

N =

A

total number of individuals

65
Q

genotype frequency = f(Aa) =

A

number of Aa individuals / N

66
Q

genotype frequency = f(aa) =

A

number of aa individuals / N

67
Q

allele frequency = p = f(A) =

A

2nAA + nAa / 2N

68
Q

allele frequency = q = f(a) =

A

2naa + nAa / 2N

69
Q

X-linked = p = f(XA) =

A

2nXAXA + nXAXa + nXAY / 2n females + n male

70
Q

X-linked = q = f(Xa) =

A

2nXaXa + nXAXa + nXaY / 2n females + n male

71
Q

the hardy-weinberg equilibrium

A

describes the effect of reproduction on genotypic and allelic frequencies

72
Q

hardy-weinberg equilibrium: generally safe assumptions

A
  • diploid
  • sexual reproduction
  • non-overlapping generations
  • bi-allelic
  • easy allele frequencies in males and females
73
Q

hardy-weinberg equilibrium: major evolutionary forces that affect allele frequencies

A
  • random mating
  • no migration
  • no mutation
  • no natural selection
  • no drift (large population)
74
Q

hardy-weinberg equilibrium: predictions

A
  1. allele frequencies do not change
  2. genotype frequencies reach equilibrium after one generation with proportions
75
Q

hardy-weinberg equilibrium: maximum frequency and minimum frequency

A
  • maximum = 1
  • minimum = 0
76
Q

hardy-weinberg equilibrium: what does a frequency of 0 mean?

A

there is no genetic diversity

77
Q

hardy-weinberg equilibrium is on a per locus basis, why would selection on chromosome 1 not impact a locus on chromosome 2?

A

independent assortment

78
Q

does mutation happen frequently? why do we need mutations?

A
  • no
  • without mutation we could not evolve or adapt
79
Q

implications of the hardy-weinberg equilibrium

A
    1. population cannot evolve if it meets HWE
    1. genotypic frequencies are determines by the allelic frequencies
    1. a single generation of random mating produces the equilibrium frequencies
80
Q

the fact that genotypes are in HWE proportions does ______ prove that the population is free from natural selection, mutation and migration. What does it mean?

A
  • NOT
  • it means only that these forces have not acted since the last time random mating took place
81
Q

positive assortative mating

A

tendency for like individuals to mate

82
Q

negative assortative mating

A

tendency for unlike individuals to mate

83
Q

outcrossing

A

preferential mating between unrelated individuals

84
Q

inbreeding

A

preferential mating between related individuals (leads to increased homozygosity)

85
Q

does inbreeding change allele frequency?

A

NO

86
Q

alleles identical by state

A

originated from different chromosomes (no relation)

87
Q

alleles identical by descent

A

two copies of the chromosome are descended from the same copy in a common ancestor

88
Q

mutation

A

ultimate source of variation

89
Q

migration: equation

A
  • q2 = q1(m) + q2(1-m)
  • m=portion of migrants
  • q1=migrating
  • q2=not migrating
90
Q

what does migration cause

A
  1. causes the allele frequencies of two populations to become more similar
  2. adds genetic variation to population
91
Q

genetic drift

A

sampling error arises when gametes unite to produce progeny

92
Q

when we sample individuals, we are sampling ___________

A

chromosomes

93
Q

the amount of genetic drift can be estimated from the _________ ___ _______ _______

A

variance in allelic frequency (sp^2=pq/2N)

94
Q

what is the result of an allelic drift?

A

allelic frequencies in the different populations diverges and often become fixed for one allele or the other

95
Q

causes of allelic drift

A
  • reduced sampling size
  • founder effect
  • bottleneck
96
Q

all genetic drift arises from ___________ _______

A

sampling error

97
Q

founder effect

A

establishment of a population by a small number of individuals

98
Q

bottleneck

A

when a population undergoes a drastic reduction in size

99
Q

effects of drift

A
  • change in allelic frequencies within a population
  • reduce genetic variation within a population
  • different populations diverge genetically from one another over time
100
Q

what suggests populations can evolve through random chance?

A

genetic drift

101
Q

natural selection

A

takes place when individuals with adaptive traits produce a greater number of offspring than do individuals not carrying such traits

102
Q

the effect of natural selection on the gene pool of a population depends on the _________ values of the genotypes in the population

A

fitness

103
Q

fitness (W)

A
  • the relative reproductive success of a genotype
  • ranges from 0 to 1
104
Q

selection coefficient (s)

A

the relative intensity of selection against genotype

105
Q

selection coefficient (s) equation

A

1 - W

Genetics (10 decks)

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