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Pre-Vet 2 > 9. Quantitative Genetics > Flashcards

9. Quantitative Genetics Flashcards

1
Q

Do all genes exhibit complete dominance

A

No incomplete penetrance and variable expressivity, epistatic interactions, polygenic traits - assort independently, producing many possible genotypes, environmental influences

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2
Q

can genetic and non genetic variation alter the phenotype

A

yes due to multifactorial traits

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3
Q

are phenotypes quantitative or qualitative

A

quantitative = showing a continuous phenotypic variation - usually described in units of measurements

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4
Q

quantitative traits

A
  • continuous variation
  • phenotypic variation is continuous along a range
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5
Q

genetic potential - what is it and which?

A

quantitative traits
- genotypes and alleles present give the maximum phenotypic expression for the individual (ex. tall parents have tall kids)
-environmental and developmental factors may also influence and contribute to phenotypic variation
(diet, prenatal care, postpartum care)

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6
Q

Major genes

A

in polygenic traits - these are genes that contribute to the trait more than others

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7
Q

modifier genes

A
  • in polygenic traits - contributing a small effect to the phenotype
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8
Q

ex of major and modifier genes

A

eye colour
major: OCA2 ( iris and skin colour - melanin) and HERC2 (regulates OCA2 expression)
modifer: the other genes in eye colour

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9
Q

conditions to using the binomial expansion

A
  • diploid , 2 alleles/gene, with even allele freq.
  • random mating or cross multi-locus heterozygotes
  • alleles only have additive effect on the phenotype
  • no linkage between genes
  • no interactions between genes
  • no environmental effects
  • discrete phenotypic categories
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10
Q

additive genes

A
  • some polygenic traits do not have specific indiivdual genes that exert major gene effects
  • these traits have a continuous phenotypic range that results from incremental contributions from multiple genes
  • each allele has its own quantitative balue
  • more than 1 genotype can contribute to the same phenotype
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11
Q

multi-gene hypothesis

A

By Nilsson-Ehle - segregation of alleles from multiple genes contribute to phenotypic variation

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12
Q

Edward East conclusion

A

corolla tube length was multi-gene but also influenced by nongenetic effects because theres variation

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13
Q

What else can affect phenotypes besides heredity

A

environment!

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14
Q

No GxE interaction
Some GxE interation
Extensive GxE interaction

A

none: F2 produces discontinuous 1:2:1 genotypic freq.
some: some overall in phenotypes
extensive: lots of phenotypic overlap/spread

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15
Q

Frequency distribution

A
  • needed to quantify phenotypic variation
  • shows the values of the trait on a quantitative scale
  • represents the proportion of variation in the sample which is used to estimate the variation in the population
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16
Q

mean, mode, median, variance, sd

A

mean - average
mode - most common
median - middle value
variance - the spread around the mean
sd - deviation from the mean in the same units as the scale of measurement

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17
Q

Vp vs Vg vs Ve

A

Vp = total phenotypic variance of a quantitative trait
Vg = proportion of the variance due to genotypes
- vg = 0 if inbred
Ve = proportion of the variance due to environmental factors
Equation: Vp = Vg+Ve

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18
Q

Other types of variance in Vg

A

Va = additive variance - additive effects of all alleles contributing to a trait - results from incomplete dominance
Vd = dominant variance - variance resulting from dominant relationships in which alleles of a heterozygote produce phenotype that is not in between the homozygotes
Vi = interactive variance - epistatic effects between alleles on different genes
equation: Vg = Va + Vd + Vi

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19
Q

familial traits

A

shared by family members for any reasons

20
Q

heritable traits

A

similar in family members due to shared genes

21
Q

heritability - high vs low

A

proportion of a phenotypic variation that is due to genetic variation
- high: most of the phenotypic variation is due to genetic variation -
- low: most of the phenotypic variation is not due to inherited genetic variation - mostly environment then

22
Q

2 types of heritability

A

Broad sense heritability (H^2) = estimates the proportion of phenotypic variation that is due to total genetic variation - H^2 = Vg/Vp - between 0-1
Narrow sense heritability (h^2) = estimates the proportion of phenotypic variation that is due to additive variation - h^2 = Va/Vp - between 0-1

23
Q

Important notes about heritability

A
  • which genetic differences contribute to phenotypic variation of a trait
  • NOT which genes control a trait or how much of the trait is controlled by gene action
24
Q

Example of broad sense heritability

A

Cave fish by wilkins
- used BSH to describe the genetic contribution to eye tissue
- dark cave - less eye tissue
- above ground - more eye tissue
- calculated and found that 90% of the phenotypic variation in eye size was due to genetic variation

25
Q

What do twins prove in heritability

A

Identical twins can look exactly alike as kids but when they grow up can look so different - due to environmental factors!

26
Q

Identical twins

A
  • single fertilization event, splitting of the fertilized embryo, share all alleles, broad sense heritability is solely due to environment since their genes are exactly the same, Vp =Ve
27
Q

Fraternal twins

A
  • two independent fertlization event, produced 2 independent zygotes, born at the same time but no genetically different than normal siblings, share an average of 50% of their alleles
    Vp = Ve + 1/2Vg
28
Q

Dependability/results of twin studies and heritability

A
  • prone to error
  • compare mz twins to same sex dz twins
  • identical twins have a stronger shared maternal effect, treatment of twins, similar interactions between gene and environment than fraternal twins
29
Q

Concordance vs Discordance

A

concordance = % of twin pairs who have the same phenotype for a trait
discordance = % of twin pairs who have different phenotypes

30
Q

Twin studies: if phenotypic variation is genetic and not genetic

A

100% genetic: MX should always be concordant - regardless if theyre raised together or not
DZ = 50% concordant with phenotype

not genetic: MZ and DZ will have equal concordance in their trait

31
Q

Concordance in twins depending on influence

A
  • MZ will have higher concordance values than DZ in traits with strong genetic influence
  • MZ and DZ will have equal concordance values in traits with strong environmental influence
32
Q

Are behavioural conditions subject to genetic influence?

A
  • known to be true
33
Q

narrow sense heritability and slopes on graphs

A

the steeper the slope, the more heritable the trait

34
Q

Higher values of narrow sense heritablity means what

A

correlated with a greater degree of response to selection

35
Q

selection differential (S)

A
  • measures the difference between the population mean value for a trait and the mean value for a trait for the mating portion of the population
    S = mean mating - mean population
36
Q

selection response (R)

A
  • depends on the selection differential can be passed to progeny
    R = S(h^2)
37
Q

Ex) mean pop = 37.5 and mean mating = 42, selection differntial = ?

A

4.5 cm

38
Q

Ex) In corn height, mean pop = 37.5, mean mating = 42, h^2 = .70 and S = 4.5, R = ?

A

3.15 cm - under stable growth conditions, progeny are expected to have a height equal to the population average of 40.65cm

39
Q

Importance of genetic correlations

A
  1. genetic correlations influence responses to selection
  2. genetic correlations are important in breeding
  3. genetic correlations are important in evolution
40
Q

M, Ms, M’

A

M = mean phenotype of parental population
Ms = mean phenotype selected for mating
M’ = mean phenotype of offspring after selection

41
Q

Higher heritability in relation to selection response

A

high heritability = higher selection response

42
Q

Directional selection

A
  • mean phenotypic value is shifted in one direction
  • one extreme of the phenotype is favoured
  • narrows phenotypic range
43
Q

Stabilising selection

A
  • favours an intermediate phenotype over the extreme phenotypes
  • reduces phenotypic variance without changing the mean
44
Q

Disruptive selection

A
  • both extreme phenotypes are favoured over the intermediate
  • increases phenotypic variation without changing the mean
  • potential phenotypic split in population (looks like a camels back on a graph)
45
Q

qualitative traits

A
  • discrete categories
  • they display a discontinuous phenotypic range
  • lead to predictable phenotypes

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