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Genetics Test 5 > 36 Quantitative Genetics > Flashcards

36 Quantitative Genetics Flashcards

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
types of heritability
broad-sense | narrow sense
26
broad sense heritability
H^2 = Vg/Vp proportion of phenotypic variance due to genetic effect
27
narrow sense heritability
h^2 = Va/Vp proportion of phenotypic variance due to additive genetic effects
28
heritability = 0
all Vp is due to environmental variance
29
heritability = 1
all Vp is due to genetic variance
30
Will higher or lower heritability lead to increase progress in a selection program?
higher
31
Ve
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
phenotypic variance is estimated by
the variance in F2 since if has all possible genotypes V(F2) = Vp = Vg+ Ve
33
Assume environmental variance in F2 is...
the same as the previous generation
34
broad sense heritability is better for asexual or sexual plants
asexual
35
response to selection
extent to which the characteristics change over a generation R = xbar1 - xbar0
36
selection differential
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
limits to selection response
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
Why does progress from selection level off?
often because the population is approaching a biological limiting factor
39
Why did corn with varying degrees of oil level off?
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
Why did drosophila with varying number of bristle level off
the number increased for many generations and then leveled off as it approached a biological limiting factor - likely room for the bristles
41
pleiotropy
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
how does pleiotropy impact breeding
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
QTL
quantitative trait loci | identified by linkage analysis between the trait and molecular markers
44
if the inheritance of a genetic marker is associated with the inheritance of a quantitative trait, the marker must be...
linked to a QTL involved in that trait
45
SNPs
single nucleotide polymorphisms
46
common markers used to identify QTL
SNPs
47
GWAS
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
DGRP
drosophila genetic reference panel developed to help identify QTLs
49
mouse collaborative cross
used to identify QTLs
50
limitations to heritability
- 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
monozygotic
identical twins
52
dizygotic
ferternal twins
53
concordant
twins same for trait
54
discordant
twins differ for trait
55
% concordance indicates...
a percentage of that twin group that showed the same phenotype
56
concordance can be expressed as...
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
High MZ: Low DZ
indicates significant role of the variance of genetic effects in the phenotypic variance
58
similar MZ and DZ
indicates a lot of variation is due to variance in environmental effects
59
low MZ but still much higher than DZ
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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