Topic 9: Quantitative Genetics

Question 1

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

Answer 1

polygenic traits

Question 2

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

Answer 2

multifactorial traits

Question 3

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

Answer 3

quantitative

Question 4

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

Answer 4

qualitative, discontinuous (lead to predictable phenotypic ratios)

Question 5

________ traits have _________ variation

Answer 5

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

Question 6

quantitative traits have ___________

Answer 6

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)

Question 7

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

Answer 7

major genes

Question 8

________ genes: contribute to a trait in small amounts

Answer 8

modifier genes

Question 9

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

Answer 9

eye colour

Question 10

number of alleles is denoted by what variable?

Answer 10

n (also known as the number of events)

Question 11

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?

Answer 11

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

Question 12

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

Answer 12

additive genes (also contributing genes)

Question 13

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

Answer 13

multi-gene hypothesis

Question 14

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)

Answer 14

true!

Question 15

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

Answer 15

tobacco

Question 16

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

Answer 16

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

Question 17

______________: values of a trait on a quantitative scale

Answer 17

frequency distribution (use this to quantify phenotypic variation!)

Question 18

______: small portion of a population

Answer 18

sample

Question 19

__________: what a sample represents

Answer 19

population

Question 20

mean: ______

Answer 20

average

Question 21

Mode: _________

Answer 21

most common value in the distribution

Question 22

median: __________

Answer 22

the middle value of the distribution

Question 23

variance: ____________

Answer 23

the spread in the distribution around the mean

Question 24

standard deviation: ____________

Answer 24

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

Question 25

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

Answer 25

Vp

Question 26

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

Answer 26

Vg

Question 27

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

Answer 27

Ve

Question 28

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

Answer 28

Vp = Vg + Ve

Question 29

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

Answer 29

additive variance

Question 30

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

Answer 30

dominant variance

Question 31

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

Answer 31

interactive variance

Question 32

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

Answer 32

Vg = Va + Vd + Vi

Question 33

_______ traits: shared by family members for any reasons

Answer 33

familial traits

Question 34

_______ traits: similar in family members due to shared genes

Answer 34

heritable genes

Question 35

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

Answer 35

heritability

Question 36

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

Answer 36

true!!

Question 37

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

Answer 37

broad sense heritability

Question 38

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

Answer 38

narrow-sense heritability

Question 39

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

Answer 39

true

Question 40

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

Answer 40

broad sense heritability

Question 41

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!

Answer 41

twins!

Question 42

_________ twins = identical twins

Answer 42

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

Question 43

______ twins = fraternal twins

Answer 43

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

Question 44

twins studied usually compare what kind of twins?

Answer 44

identical twins vs. same-sex fraternal twins

Question 45

true/false: twin studies can be prone to error

Answer 45

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

Question 46

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

Answer 46

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

Question 47

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

Answer 47

discordance

Question 48

___________ (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

Answer 48

selection differential

Question 49

___________ (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

Answer 49

selection response

Question 50

genetic correlations are important to...

Answer 50

breeding, evolution, influence responses to selection

Question 51

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

Answer 51

directional selection

Question 52

_______ selection: favours an intermediate phenotype over the extreme phenotypes

Answer 52

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

Question 53

_______ selection: both extreme phenotypes are favoured over the intermediate

Answer 53

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