Population Genetics Flashcards
Gene
a segment of DNA whose nucleotide sequence codes for proteins, codes for RNA, or regulates the expression of other genes
Allele
one of any number of alternative forms of the DNA sequence of the same locus
Locus
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
Punnett square
A method of predicting the results of a genetic cross by arranging the gametes of each parent at the edges of a square
Genotype
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
Phenotype
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)
Dominant
an allele that produces the same phenotype whether it is paired with an identical allele or a different allele (that is, a heterozygotic state)
Recessive
an allele that produces its characteristic phenotype only when it is paired with an identical allele (that is, in homozygous states)
Hardy-Weinberg equilibrium
null hypothesis
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
non-random mating
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
genetic drift
Changes in gene frequencies from generation to generation as a result of random (chance) processes
gene flow
Exchange of genes between populations through migration of individuals or movements of gametes
Mutation
any change to the genomic sequence of an organism
chi-square test
A statistical test used to assess whether the frequencies of observations in different categories are consistent with a hypothesized frequency distribution
Microevolutionary forces
Natural selection
Non-random mating
Genetic drift
Gene flow
Mutation
quantitative traits
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
Polygenic
the cumulative action of many genes
narrow-sense heritability (h2)
the proportion of the total phenotypic variance of a trait attributable to the additive effects of alleles (the additive genetic variance)
additive genetic variance
the component of variance that causes offspring to resemble their parents, and it causes populations to evolve predictably in response to selection
allele fixation
where an allele becomes fully established in a population
Fitness
success of an organism at surviving and reproducing, and thus contributing offspring to future generations
inheritance system
Dominant
an allele that determines the phenotype in an individual who is heterozygous for it and a different (recessive) allele
Recessive
an allele that does not determine phenotype in an individual who is heterozygous for it and a different (dominant) allele
Additive
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)
heterozygote advantage
occurs when selection favors heterozygote individuals over either the dominant homozygote or the recessive homozygote
directional selection
favors individuals on one end of the distribution of phenotypes present in a population
stabilizing (or purifying) selection
favors individuals in the middle of the distribution of phenotypes present in a population (for example, by acting against individuals at either extreme)
disruptive selection
favors individuals at the tails of the distribution of phenotypes present in a population (for example, by acting against individuals with intermediate trait values)
breeder’s equation
R = h2 x S : phenotypic variation that influences fitness (S) and the ability to transmit those phenotypic characteristics to offspring (h2)
genetic drift
evolution arising from random changes in the genetic composition of a population from one generation to the next
Bottleneck
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
founder effect
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
sampling effect
the effect of introducing into a new environment a selected sub-sample of a species’ many possible genotypes
FST
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
inbreeding depression
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
Heterozygosity
the proportion of heterozygotes among all genotypes for a genetic marker in a population
allelic richness
a measure of genetic diversity indicative of a population’s long-term potential for adaptability and persistence
gene flow
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
Migration
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
genetic drift
evolution arising from random changes in the genetic composition of a population from one generation to the next
natural selection
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
