Population Genetics

Question 1

Gene

Answer 1

a segment of DNA whose nucleotide sequence codes for proteins, codes for RNA, or regulates the expression of other genes

Question 2

Allele

Answer 2

one of any number of alternative forms of the DNA sequence of the same locus

Question 3

Locus

Answer 3

the specific location of a gene or piece of DNA sequence on a chromosome. When mutations modify the sequence at a locus, they generate new alleles—variants of a particular gene or DNA region. Alleles are mutually exclusive alternative states for a genetic locus

Question 4

Punnett square

Answer 4

A method of predicting the results of a genetic cross by arranging the gametes of each parent at the edges of a square

Question 5

Genotype

Answer 5

the genetic makeup of an individual. Although a genotype includes all the alleles of all the genes in that individual, the term is often used to refer to the specific alleles carried by an individual for any particular gene

Question 6

Phenotype

Answer 6

an observable, measurable characteristic of an organism. A phenotype may be a morphological structure (for example, antlers, muscles), a developmental process (for example, learning), a physiological process or performance trait (for example, running speed), or a behavior (for example, mating display)

Question 7

Dominant

Answer 7

an allele that produces the same phenotype whether it is paired with an identical allele or a different allele (that is, a heterozygotic state)

Question 8

Recessive

Answer 8

an allele that produces its characteristic phenotype only when it is paired with an identical allele (that is, in homozygous states)

Question 9

Hardy-Weinberg equilibrium
null hypothesis

Answer 9

a default hypothesis that there is no relationship between two measured phenomena. By rejecting this hypothesis, scientists can provide evidence that such a relationship may exist

Question 10

non-random mating

Answer 10

mating system in which at least some individuals are more or less likely to mate with individuals of a particular genotype than with individuals of other genotypes

Question 11

genetic drift

Answer 11

Changes in gene frequencies from generation to generation as a result of random (chance) processes

Question 12

gene flow

Answer 12

Exchange of genes between populations through migration of individuals or movements of gametes

Question 13

Mutation

Answer 13

any change to the genomic sequence of an organism

Question 14

chi-square test

Answer 14

A statistical test used to assess whether the frequencies of observations in different categories are consistent with a hypothesized frequency distribution

Question 15

Microevolutionary forces

Answer 15

Natural selection
Non-random mating
Genetic drift
Gene flow
Mutation

Question 16

quantitative traits

Answer 16

a measurable phenotype that varies among individuals over a given range to produce a continuous distribution of a phenotype. Quantitative traits are sometimes called complex traits

Question 17

Polygenic

Answer 17

the cumulative action of many genes

Question 18

narrow-sense heritability (h2)

Answer 18

the proportion of the total phenotypic variance of a trait attributable to the additive effects of alleles (the additive genetic variance)

Question 19

additive genetic variance

Answer 19

the component of variance that causes offspring to resemble their parents, and it causes populations to evolve predictably in response to selection

Question 20

allele fixation

Answer 20

where an allele becomes fully established in a population

Question 21

Fitness

Answer 21

success of an organism at surviving and reproducing, and thus contributing offspring to future generations

Question 22

inheritance system

Question 23

Dominant

Answer 23

an allele that determines the phenotype in an individual who is heterozygous for it and a different (recessive) allele

Question 24

Recessive

Answer 24

an allele that does not determine phenotype in an individual who is heterozygous for it and a different (dominant) allele

Question 25

Additive

Answer 25

describes an allele that yields twice the phenotypic effect when two copies are present at a given locus than occurs when only one copy is present. Additive alleles are not influenced by the presence of other alleles (for example, there is no dominance)

Question 26

heterozygote advantage

Answer 26

occurs when selection favors heterozygote individuals over either the dominant homozygote or the recessive homozygote

Question 27

directional selection

Answer 27

favors individuals on one end of the distribution of phenotypes present in a population

Question 28

stabilizing (or purifying) selection

Answer 28

favors individuals in the middle of the distribution of phenotypes present in a population (for example, by acting against individuals at either extreme)

Question 29

disruptive selection

Answer 29

favors individuals at the tails of the distribution of phenotypes present in a population (for example, by acting against individuals with intermediate trait values)

Question 30

breeder’s equation

Answer 30

R = h2 x S : phenotypic variation that influences fitness (S) and the ability to transmit those phenotypic characteristics to offspring (h2)

Question 31

genetic drift

Answer 31

evolution arising from random changes in the genetic composition of a population from one generation to the next

Question 32

Bottleneck

Answer 32

an event in which the number of individuals in a population is reduced drastically. Even if this dip in numbers is temporary, it can have lasting effects on the genetic variation of a population

Question 33

founder effect

Answer 33

a form of genetic drift. It describes the loss of allelic variation that accompanies the founding of a new population from a very small number of individuals (a small sample of a much larger source population). This effect can cause the new population to differ considerably from the source population

Question 34

sampling effect

Answer 34

the effect of introducing into a new environment a selected sub-sample of a species’ many possible genotypes

Question 35

FST

Answer 35

measures the reduction in heterozygotes at a locus attributable to the effects of population subdivision and provides a useful way to quantify how dramatically populations have diverged in their respective allele frequencies. When FST values are near zero, then populations have very little genetic structure; allele frequencies are approximately the same from place to place. However, when local subpopulations have begun to diverge from each other, FST values increase. Populations with high FST values often have extensive spatial variation in allele frequencies from place to place, reflecting genetic differences among populations across the landscape

Question 36

inbreeding depression

Answer 36

a reduction in the average fitness of inbred individuals relative to that of outbred individuals. It arises because rare recessive alleles become expressed in a homozygous state where they can affect detrimentally the performance of individuals

Question 37

Heterozygosity

Answer 37

the proportion of heterozygotes among all genotypes for a genetic marker in a population

Question 38

allelic richness

Answer 38

a measure of genetic diversity indicative of a population’s long-term potential for adaptability and persistence

Question 39

gene flow

Answer 39

describes the movement, or migration, of alleles from one population to another; Exchange of genes between populations through migration of individuals or movements of gametes

Question 39

Migration

Answer 39

Movement by an animal that entails traveling to a different location, remaining there for a substantial length of time, and then returning—often carried out in a periodic (repeating) way year after year

Question 40

genetic drift

Answer 40

evolution arising from random changes in the genetic composition of a population from one generation to the next

Question 41

natural selection

Answer 41

a mechanism that can lead to adaptive evolution, whereby differences in the phenotypes of individuals cause some of them to survive and reproduce more effectively than others and therefore outcompete them