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Genetics > Exam 4 > Flashcards

Exam 4 Flashcards

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

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44
Q

H^2 = 0

A

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

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45
Q

H^2 = 1

A

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

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46
Q

H^2 = between 0-1

A

both genetic and environmental factors influence phenotypic variance

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47
Q

________ variance is what is able to be reproductively selected for

A

additive

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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
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49
Q

phenotypic variance equation

A

Vp = VA + VD + VI + VE + VGE

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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
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51
Q

VG equation

A

VA + VD + VI

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52
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

53
Q

why are there deviations from the expected phenotypes?

A

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

54
Q

h^2 = b

A

regression of offspring mean against mean of both parents

55
Q

response to selection

A

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

56
Q

selection differential

A

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

57
Q

limits to the response to selection

What are two reasons why a trait may cease to respond to selection?

A
  • no genetic variability
  • biological limitations
58
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
59
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

60
Q

mendelian population

A

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

61
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

62
Q

genotype frequency = f(AA) =

A

number of AA individuals / N

63
Q

N =

A

total number of individuals

64
Q

genotype frequency = f(Aa) =

A

number of Aa individuals / N

65
Q

genotype frequency = f(aa) =

A

number of aa individuals / N

66
Q

allele frequency = p = f(A) =

A

2nAA + nAa / 2N

67
Q

allele frequency = q = f(a) =

A

2naa + nAa / 2N

68
Q

X-linked = p = f(XA) =

A

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

69
Q

X-linked = q = f(Xa) =

A

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

70
Q

the hardy-weinberg equilibrium

A

describes the effect of reproduction on genotypic and allelic frequencies

71
Q

hardy-weinberg equilibrium: generally safe assumptions

A
  • diploid
  • sexual reproduction
  • non-overlapping generations
  • bi-allelic
  • easy allele frequencies in males and females
72
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)
73
Q

hardy-weinberg equilibrium: predictions

A
  1. allele frequencies do not change
  2. genotype frequencies reach equilibrium after one generation with proportions
74
Q

hardy-weinberg equilibrium: maximum frequency and minimum frequency

A
  • maximum = 1
  • minimum = 0
75
Q

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

A

there is no genetic diversity

76
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

77
Q

does mutation happen frequently? why do we need mutations?

A
  • no
  • without mutation we could not evolve or adapt
78
Q

implications of the hardy-weinberg equilibrium

A
    1. population cannot evolve if it meets HWE
    1. genotypic frequencies are determined by the allelic frequencies
    1. a single generation of random mating produces the equilibrium frequencies
79
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
80
Q

positive assortative mating

A

tendency for like individuals to mate

81
Q

negative assortative mating

A

tendency for unlike individuals to mate

82
Q

outcrossing

A

preferential mating between unrelated individuals

83
Q

inbreeding

A

preferential mating between related individuals (leads to increased homozygosity)

84
Q

does inbreeding change allele frequency?

A

NO

85
Q

alleles identical by state

A

originated from different chromosomes (no relation)

86
Q

alleles identical by descent

A

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

87
Q

mutation

A

ultimate source of variation

88
Q

migration: equation

A
  • q2 = q1(m) + q2(1-m)
  • m=portion of migrants
  • q1=migrating
  • q2=not migrating
89
Q

what does migration cause

A
  1. causes the allele frequencies of two populations to become more similar
  2. adds genetic variation to population
90
Q

genetic drift

A

sampling error arises when gametes unite to produce progeny

91
Q

when we sample individuals, we are sampling ___________

A

chromosomes

92
Q

the amount of genetic drift can be estimated from the _________ in allelic frequency

A

variance (sp^2=pq/2N)

93
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

94
Q

causes of allelic drift

A
  • reduced sampling size
  • founder effect
  • bottleneck
95
Q

all genetic drift arises from ___________ _______

A

sampling error

96
Q

founder effect

A

establishment of a population by a small number of individuals

97
Q

bottleneck

A

when a population undergoes a drastic reduction in size

98
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
99
Q

what suggests populations can evolve through random chance?

A

genetic drift

100
Q

natural selection

A

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

101
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

102
Q

fitness (W)

A
  • the relative reproductive success of a genotype
  • ranges from 0 to 1
103
Q

selection coefficient (s)

A

the relative intensity of selection against genotype

104
Q

selection coefficient (s) equation

A

1 - W

105
Q

phenotypic variance symbol

A

Vp

106
Q

Human height is a highly polygenic trait and has a high heritability.
a) If you have (or already had) children, what would be your best estimate of their adult hight before they are even born? I’m asking how you would estimate this not an actual number.
b) What basic principle of genetics allows you to make that estimate? Don’t overthink this.

A

a) the mean of the parents heights
b) diploid, half of your DNA comes from mom and half from dad

107
Q

We said that heritability cannot be calculated for an individual and heritability has no meaning for a specific individual. Why?

A

we calculate the phenotypes and genotypes based on what is shown in a larger group, it must be calculated for a population, not just an individual

108
Q

forces that change allele frequency

A
  • mutation
  • migration
  • selection
  • drift
109
Q

how does mutation change allele frequency?

A

ultimate source of variation, change allele frequency slow

110
Q

how does migration change allele frequency?

A

adds new alleles, end result is that the two populations will become more similar

111
Q

how does drift change allele frequency?

A

randomly, dictated by population size (sampling variance)

112
Q

how does selection change allele frequency?

A

fitness, ability of a genotype to produce more or less than another genotype

113
Q

migration

A

blending of populations with different frequencies until equilibrium is reached

114
Q

what do migration, mutation, selection, and drift have in common?

A

time, everything is based on times, based on generations

115
Q

evolutionary genetics

A

the study of genetic changes over time

116
Q

the raw material for genetic change is _____________

A

mutation

117
Q

molecular data advantages

A
  • quantifiable
  • can be used with all organisms
  • can compare all organisms
  • can be applied to a huge amount of genetic variation
118
Q

biological species concept

A

members of a population that actually or potentially interbreed in nature

119
Q

reproductive barriers

A

pre zygotic and postzygotic

120
Q

prezygotic (definition and types)

A

acts before a zygote has formed (ecological, temporal, mechanical, behavioral, gametic)

121
Q

postzygotic (definition and types)

A

acts after a zygote has formed (hybrid inviability, hybrid sterility, hybrid breakdown)

122
Q

speciation

A

process by which new species arise

123
Q

allopatric

A

speciation is initiated when a geographic barrier splits a population into two or more groups and prevents gene flow between those groups

124
Q

sympatric

A

speciation arises in the absence of an geographic barrier to gene flow; in this mode of speciation, reproductive isolating mechanisms evolve within a single interbreeding population

125
Q

two types of speciation

A

allopatric and sympatric

126
Q

in sympatric speciation; reproductive isolation mechanisms arise as a ______________ of genetic differentiation

A

consequence

127
Q

what does evolutionary genetics deal with?

A

populations and species, not individuals

128
Q

biological species concept: members of a population that __________ or __________ interbreed in nature

A

actually or potentially

Genetics (10 decks)

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