Chapter 7: Quantitative Genetics

Question 1

quantitative genetics

Answer 1

the study of continuous phenotypic traits and their underlying evolutionary mechanisms

Question 2

variance

Answer 2

a statistical measure of the dispersion of trait values about their mean

Question 3

narrow sense heritability (h²)

Answer 3

the proportion of the total phenotypic variance of a trait attributable to the additive effects of alleles (the additive genetic variance); we can use this to predict how phenotypes will change over time as a result of natural selection and how closely we can expect offspring to resemble parentsanswers the question: what fraction of variation is visible to selection?

Question 4

selection differential (S)

Answer 4

a measure of the strength of phenotypic selection; the selection differential describes the difference between the mean of all members of a population and the mean of the individuals that reproduce, contributing offspring to the next generation

Question 5

discrete traits

Answer 5

distinct phenotypes that are determined by a single gene (uncommon in reality)

Question 6

continuous variation

Answer 6

scale of possibilities for a phenotype (ex: height is not strictly tall/short, it can be anything from like 4 feet to 8) → this is determined by the effects of many genesheight, intelligence, skin color are all examples

Question 7

polygenic traits

Answer 7

determined by many genes and produce continuous variation (majority of traits in the real world)

Question 8

additive effects

Answer 8

seen when the phenotype of an individual is obtained simply by summing the effects of individual alleles

Question 9

heritability

Answer 9

measures what portion of variation is due to genes and what portion is due to environment (it is a ratio)

Question 10

broad sense heritability (H²)

Answer 10

defines the fraction of the total variance that is due to genetic causes

Question 11

directional selection

Answer 11

natural selection operates on a phenotype to favor one at the extremes, population allele frequency reflects this over time

Question 12

stabilizing selection

Answer 12

natural selection eliminates the phenotypes at both extremes; this is the most common type of selection

Question 13

disruptive selection

Answer 13

natural selection eliminates phenotypes in the middle of the distribution and selects for the extremes; this is rare

Question 14

strength of selection

Answer 14

quantifiable differences in reproductive success and survival of individuals with a trait → measured by selection differential