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Genetics 1 > Topic 9: Quantitative Genetics > Flashcards

Topic 9: Quantitative Genetics Flashcards

1
Q

________ traits: traits controlled by more than one gene, they assort independently and produce many possible genotypes

A

polygenic traits

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2
Q

__________ traits: “multiple factors”, such as genes and the environment

A

multifactorial traits

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3
Q

phenotypes are _______, showing a continuous phenotypic variation (traits can be described in a unit of measure)

A

quantitative

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4
Q

________ traits have discrete categories, and display a ________ phenotypic range

A

qualitative, discontinuous (lead to predictable phenotypic ratios)

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5
Q

________ traits have _________ variation

A

quantitative, continuous (phenotypic variation is continuous along a range)

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6
Q

quantitative traits have ___________

A

genetic potential (whether you reach that maximum potential is dependant on the influence of all other factors) (ex: height, if you have tall parents, you have the potential to also be tall)

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7
Q

_______ genes: genes that contribute more to the trait than others

A

major genes

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8
Q

________ genes: contribute to a trait in small amounts

A

modifier genes

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9
Q

what is an example of a quantitative trait with major and modifier genes?

A

eye colour

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10
Q

number of alleles is denoted by what variable?

A

n (also known as the number of events)

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11
Q
  1. diploid (2 allels/gene)
  2. random mating/ cross multi-locus heterozygotes
  3. contributing alleles only have an additive effect on the phenotype
  4. no linkage between the genes
  5. no interactions between the genes
  6. no environmental effects
  7. discrete phenotypic categories

these are all conditions to using what expression?

A

the binomial expression (few traits meet these assumptions, especially in natural populations)

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12
Q

_______ genes: incremental contributions from multiple genes, have a continuous phenotypic range

A

additive genes (also contributing genes)

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13
Q

Hermann Nilsson-Ehle proposed the _________ hypothesis, segregation of alleles from multiple genes contributes to phenotypic variation

A

multi-gene hypothesis

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14
Q

true/false: the more phenotypes that occur along the phenotypic range, the narrower the frequency distribution of each category… the more classes we have, the more it appears to be blending (colours become more and more similar to each other)

A

true!

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15
Q

in 1916, Edward East conducted experiments on ______ plants, concluding that the tube-length was multi-gene but also influenced by nongenetic effects (environment)

A

tobacco

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16
Q

true/false: gene-environment interaction doesn’t result in phenotypic spread

A

false! it does, when there is extensive GxE interactions there is SIGNIFICANT phenotypic overlap

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17
Q

______________: values of a trait on a quantitative scale

A

frequency distribution (use this to quantify phenotypic variation!)

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18
Q

______: small portion of a population

A

sample

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19
Q

__________: what a sample represents

A

population

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20
Q

mean: ______

A

average

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21
Q

Mode: _________

A

most common value in the distribution

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22
Q

median: __________

A

the middle value of the distribution

23
Q

variance: ____________

A

the spread in the distribution around the mean

24
Q

standard deviation: ____________

A

deviation from the mean in the same units as the scale of measurement

25
Q

_____: phenotypic variance of a quantitative trait (its a variable)

A

Vp

26
Q

Genes (_____): proportion of the variance due to genotypes

A

Vg

27
Q

Environment (____): proportion of the variance due to environmental factors

A

Ve

28
Q

how do Vp, Vg, and Ve relate in a formula?

A

Vp = Vg + Ve

29
Q

________________ (Va): additive effects of all alleles contributing to a trait

A

additive variance

30
Q

___________ (Vd): variance resulting from dominant relationships in which alleles of a heterozygote produce phenotype not in between the homozygotes (non-additive alleles)

A

dominant variance

31
Q

______ (Vi): epistatic effects between alleles on different genes

A

interactive variance

32
Q

how do Vg, Va, Vd, and Vi relate in a formula?

A

Vg = Va + Vd + Vi

33
Q

_______ traits: shared by family members for any reasons

A

familial traits

34
Q

_______ traits: similar in family members due to shared genes

A

heritable genes

35
Q

__________: proportion of phenotypic variation that is due to genetic variation

A

heritability

36
Q

true/false: heritability differs from trait to trait, and in the same trait between different environments

A

true!!

37
Q

____________ heritability (H^2): estimates the proportion of phenotypic variation that is due to total genetic variation

A

broad sense heritability

38
Q

_________ heritability (h^2): estimates the proportion of phenotypic variation that is due to additive gene variation (Va)

A

narrow-sense heritability

39
Q

true/false: heritability is NOT an indication of the mechanism by which genes control a trait, or how much of the trait is controlled by gene action

A

true

40
Q

Dr. Horst Wilkens did a study of cave fish in 1988, and used ________ heritability to describe the genetic contribution to eye tissue

A

broad sense heritability

41
Q

what is the one human case where we can study broad sense heritability? since we need the mating and environmental influences to be controlled this is rare!

A

twins!

42
Q

_________ twins = identical twins

A

monozygotic, they share all the same alleles so we can assume that broad sense heritability is due solely to environmental factors !! Vp=Ve

43
Q

______ twins = fraternal twins

A

dizygotic twins, share an average of ~50% of their alleles so… Vp = Ve + 1/2 Vg

44
Q

twins studied usually compare what kind of twins?

A

identical twins vs. same-sex fraternal twins

45
Q

true/false: twin studies can be prone to error

A

true!
maternal effects are stronger in identical compared to fraternal
identical twins are treated more similarly compared to fraternal
great similarity in interactions between genes + environmental factors in identical vs. fraternal

46
Q

____________: % of twin pairs in which both members of the pair have the same phenotype for a trait

A

concordance (NOTE: a high concordance value does not indicate strong genetic influence!!)

47
Q

_________: % of twin pairs in which both members have different phenotypes

A

discordance

48
Q

___________ (S): 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

A

selection differential

49
Q

___________ (R): depends on the extent to which the difference between the mating trait mean value and the population trait mean value can be passed to progeny

A

selection response

50
Q

genetic correlations are important to…

A

breeding, evolution, influence responses to selection

51
Q

_______ selection: mean phenotypic value is shifted in one direction because one extreme pf the phenotype is favoured

A

directional selection

52
Q

_______ selection: favours an intermediate phenotype over the extreme phenotypes

A

stabilizing selection (reduces phenotypic variation W/O changing the mean)

53
Q

_______ selection: both extreme phenotypes are favoured over the intermediate

A

disruptive selection (increases phenotypic variation W/O changing the mean)

Genetics 1 (11 decks)

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