Topic 9: Quantitative Genetics Flashcards
________ traits: traits controlled by more than one gene, they assort independently and produce many possible genotypes
polygenic traits
__________ traits: “multiple factors”, such as genes and the environment
multifactorial traits
phenotypes are _______, showing a continuous phenotypic variation (traits can be described in a unit of measure)
quantitative
________ traits have discrete categories, and display a ________ phenotypic range
qualitative, discontinuous (lead to predictable phenotypic ratios)
________ traits have _________ variation
quantitative, continuous (phenotypic variation is continuous along a range)
quantitative traits have ___________
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)
_______ genes: genes that contribute more to the trait than others
major genes
________ genes: contribute to a trait in small amounts
modifier genes
what is an example of a quantitative trait with major and modifier genes?
eye colour
number of alleles is denoted by what variable?
n (also known as the number of events)
- diploid (2 allels/gene)
- random mating/ cross multi-locus heterozygotes
- contributing alleles only have an additive effect on the phenotype
- no linkage between the genes
- no interactions between the genes
- no environmental effects
- discrete phenotypic categories
these are all conditions to using what expression?
the binomial expression (few traits meet these assumptions, especially in natural populations)
_______ genes: incremental contributions from multiple genes, have a continuous phenotypic range
additive genes (also contributing genes)
Hermann Nilsson-Ehle proposed the _________ hypothesis, segregation of alleles from multiple genes contributes to phenotypic variation
multi-gene hypothesis
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)
true!
in 1916, Edward East conducted experiments on ______ plants, concluding that the tube-length was multi-gene but also influenced by nongenetic effects (environment)
tobacco
true/false: gene-environment interaction doesn’t result in phenotypic spread
false! it does, when there is extensive GxE interactions there is SIGNIFICANT phenotypic overlap
______________: values of a trait on a quantitative scale
frequency distribution (use this to quantify phenotypic variation!)
______: small portion of a population
sample
__________: what a sample represents
population
mean: ______
average
Mode: _________
most common value in the distribution
median: __________
the middle value of the distribution
variance: ____________
the spread in the distribution around the mean
standard deviation: ____________
deviation from the mean in the same units as the scale of measurement
_____: phenotypic variance of a quantitative trait (its a variable)
Vp
Genes (_____): proportion of the variance due to genotypes
Vg
Environment (____): proportion of the variance due to environmental factors
Ve
how do Vp, Vg, and Ve relate in a formula?
Vp = Vg + Ve
________________ (Va): additive effects of all alleles contributing to a trait
additive variance
___________ (Vd): variance resulting from dominant relationships in which alleles of a heterozygote produce phenotype not in between the homozygotes (non-additive alleles)
dominant variance
______ (Vi): epistatic effects between alleles on different genes
interactive variance
how do Vg, Va, Vd, and Vi relate in a formula?
Vg = Va + Vd + Vi
_______ traits: shared by family members for any reasons
familial traits
_______ traits: similar in family members due to shared genes
heritable genes
__________: proportion of phenotypic variation that is due to genetic variation
heritability
true/false: heritability differs from trait to trait, and in the same trait between different environments
true!!
____________ heritability (H^2): estimates the proportion of phenotypic variation that is due to total genetic variation
broad sense heritability
_________ heritability (h^2): estimates the proportion of phenotypic variation that is due to additive gene variation (Va)
narrow-sense heritability
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
true
Dr. Horst Wilkens did a study of cave fish in 1988, and used ________ heritability to describe the genetic contribution to eye tissue
broad sense heritability
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!
twins!
_________ twins = identical twins
monozygotic, they share all the same alleles so we can assume that broad sense heritability is due solely to environmental factors !! Vp=Ve
______ twins = fraternal twins
dizygotic twins, share an average of ~50% of their alleles so… Vp = Ve + 1/2 Vg
twins studied usually compare what kind of twins?
identical twins vs. same-sex fraternal twins
true/false: twin studies can be prone to error
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
____________: % of twin pairs in which both members of the pair have the same phenotype for a trait
concordance (NOTE: a high concordance value does not indicate strong genetic influence!!)
_________: % of twin pairs in which both members have different phenotypes
discordance
___________ (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
selection differential
___________ (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
selection response
genetic correlations are important to…
breeding, evolution, influence responses to selection
_______ selection: mean phenotypic value is shifted in one direction because one extreme pf the phenotype is favoured
directional selection
_______ selection: favours an intermediate phenotype over the extreme phenotypes
stabilizing selection (reduces phenotypic variation W/O changing the mean)
_______ selection: both extreme phenotypes are favoured over the intermediate
disruptive selection (increases phenotypic variation W/O changing the mean)
