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Genetics Test 5 > 36 Quantitative Genetics > Flashcards

36 Quantitative Genetics Flashcards

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1
Q

Quantitative traits…

A
  • have continuous variation
  • have no distinct F2 classes
  • often assume normal distribution
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2
Q

Multifactor Hypothesis

A
  • Edward East
  • expression depends on the additive effects of a number of genes
  • the effect of each gene is small
  • environment plays an important role in the expression of traits
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3
Q

What is the effect of the environment on the curve of frequency of phenotype classes?

A

it smooths the curve

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4
Q

environmental effects allow…

A

one genotype to produce multiple phenotypes

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5
Q

variance

A

average squared deviation from the mean

related to the width of the curve - more narrow, less variance

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6
Q

wider curve equals

A

more variation

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7
Q

the units for standard deviation are the same as

A

those for the original measure of the trait

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8
Q

threshold traits

A

quantitative traits with only two phenotypes

an accumulation of factors pushes the phenotype over the limit to the second trait

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9
Q

Phenotype =

A

genetic + environment effect

P = G+ E

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10
Q

Genetic effect =

A

additive + dominance effect

G = A + D

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11
Q

additive effect

A

average effect of substituting A for a in genotype

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12
Q

dominance effect

A

due to the fact that sometimes the heterozygote is not halfway between the two homozygotes

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13
Q

when does D (for dominance effect) equal 0

A

if the value of Aa is exactly between the values of AA and aa

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14
Q

complete dominance

A

the heterozygote and BB have the same value

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15
Q

Vp

A

s^2
phenotypic variance
variance calculated from the measurements of the phenotypes of the individuals in the population

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16
Q

Vg

A

genetic variance

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17
Q

Ve

A

environmental variance

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18
Q

Va

A

additive genetic variance

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19
Q

Vd

A

dominance genetic variance

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20
Q

Vp =

A

Vg + Ve

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21
Q

Vg =

A

Va + Vd

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22
Q

Vi

A

epistatic interaction

will not be included in our calculations

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23
Q

Vge

A

interaction between the gene and its environment

will not be included in our calculations

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24
Q

heritability

A

proportion of the phenotypic variance due to genetic effects

used to predict rate and amount of selection response in a breeding program

25
Q

types of heritability

A

broad-sense

narrow sense

26
Q

broad sense heritability

A

H^2 = Vg/Vp

proportion of phenotypic variance due to genetic effect

27
Q

narrow sense heritability

A

h^2 = Va/Vp

proportion of phenotypic variance due to additive genetic effects

28
Q

heritability = 0

A

all Vp is due to environmental variance

29
Q

heritability = 1

A

all Vp is due to genetic variance

30
Q

Will higher or lower heritability lead to increase progress in a selection program?

A

higher

31
Q

Ve

A

all variation in the parental and F1 generations
each generation has only one genotype - pure bred line

the best estimate of variance due to environmental effects

V(parent1) + V(parent2) + V(F1)/3

32
Q

phenotypic variance is estimated by

A

the variance in F2 since if has all possible genotypes

V(F2) = Vp = Vg+ Ve

33
Q

Assume environmental variance in F2 is…

A

the same as the previous generation

34
Q

broad sense heritability is better for asexual or sexual plants

A

asexual

35
Q

response to selection

A

extent to which the characteristics change over a generation

R = xbar1 - xbar0

36
Q

selection differential

A

the difference between the average of the initial population and the average of those selected to be parents

the potential for change

S = Xbars - xbar0

37
Q

limits to selection response

A

selection response may decline after selecting for a particular characteristic in a population for a longer period of time because…

  • genetic variation is bein lost
  • extreme types may not be healthy
  • two desirable traits may be negatively correlated making it difficult to select for both
38
Q

Why does progress from selection level off?

A

often because the population is approaching a biological limiting factor

39
Q

Why did corn with varying degrees of oil level off?

A

the low oil content approach a limit as a certain amount of oil must be present for growth

the high oil content continued to grow

40
Q

Why did drosophila with varying number of bristle level off

A

the number increased for many generations and then leveled off as it approached a biological limiting factor - likely room for the bristles

41
Q

pleiotropy

A

a change in value for one trait is accompanied by a change in value for another trait due to a gene that affects on also affects the other

can be pos or neg correlation

42
Q

how does pleiotropy impact breeding

A

milk cow example

milk yield and milk fat % are correlated - as milk yield increases, milk fat decreases and visa versa - if you select for one, you lose the other

pleiotropy may create a challenge to overcome

43
Q

QTL

A

quantitative trait loci

identified by linkage analysis between the trait and molecular markers

44
Q

if the inheritance of a genetic marker is associated with the inheritance of a quantitative trait, the marker must be…

A

linked to a QTL involved in that trait

45
Q

SNPs

A

single nucleotide polymorphisms

46
Q

common markers used to identify QTL

A

SNPs

47
Q

GWAS

A

genome-wide association studies

associate a trait and gene markers in a biological population as opposed to controlled crosses

use molecular genetics to scan entire genome for regions that show statistical sig for a trait

48
Q

DGRP

A

drosophila genetic reference panel

developed to help identify QTLs

49
Q

mouse collaborative cross

A

used to identify QTLs

50
Q

limitations to heritability

A
  • does not say how much genes affects the trait, but how much they affect the variation in the trait
  • not seen in an individual - only in population
  • specific to a particular population in a particular environment only
  • assumes that the environment for related individuals is not more similar than the environment for unrelated peoples
51
Q

monozygotic

A

identical twins

52
Q

dizygotic

A

ferternal twins

53
Q

concordant

A

twins same for trait

54
Q

discordant

A

twins differ for trait

55
Q

% concordance indicates…

A

a percentage of that twin group that showed the same phenotype

56
Q

concordance can be expressed as…

A
  1. % concordance
  2. the ratio of MZ:DZ for a particular trait where the numbers in the ratio are the % concordance for each twin group

can be used to estimate heritability

57
Q

High MZ: Low DZ

A

indicates significant role of the variance of genetic effects in the phenotypic variance

58
Q

similar MZ and DZ

A

indicates a lot of variation is due to variance in environmental effects

59
Q

low MZ but still much higher than DZ

A

indicate genetic predisposition, but variance due to environmental factor is importance in the variance of the phenotypes for this trait

Genetics Test 5 (5 decks)

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