Ch 18 Population Genetics Flashcards
genetic rescue
introduction of new genetic variation into an inbred population often dramatically improves the health of the population and can increase its chance of long-term survival
Mendilian population
a group of interbreeding, sexually reproducing individuals that have a common set of genes
gene pool
common set of genes
population genetics
the branch of genetics that studies the genetic makeup of groups of individuals and how a group’s genetic composition changes with time
also the study of evolution
genotype frequency
to calculate, add up the number of individuals possessing a genotype and divide by the total number of individuals in the sample (N)
sum of all genotypic frequencies always equal 1
allelic frequencies
gene pool of a population can also be described in terms of this
can be calculated from 1) numbers or 2) frequencies of the genotypes
Hardy-Weinberg Law
a mathematical model that evaluates the effect of reproduction on the genotypic and allelic frequencies of a population
Assumptions: if a population is large, randomly mating, and not affected by mutation, migration or natural selection, then
Prediction 1: the allelic frequencies of a population do not change; and
Prediction 2: the genotypic frequencies stabilize after one generation in the proportions p^2, 2pq, and q^2 where p equals the frequency of allele A and q equals the frequency of allele a
Hardy-Weinberg equilibrium
when genotypes are in the expected proportions of p^2, 2pq, and q^2, the population is said to be in this
inbreeding
one form of nonrandom mating which is preferential mating between related individuals
leads to an increase in the proportion of homozygotes and a decrease in the proportion of heterozygotes in a population
processes that bring about change in allelic frequencies
mutation, migration, genetic drift (random effects due to small population size) and natural selection
equilibrium
a point at which there is no change in the allelic frequencies of a population
migration or gene flow
the influx of genes from other populations
overall effect: 1) it prevents populations from becoming genetically different from one another and 2) it increases genetic variation within populations
sampling error
deviation from an expected ratio due to limited sample size
arises when gametes unite to produce progeny
genetic drift
changes in allelic frequencies
effective population size (Ne)
population geneticists define population size as the equivalent number of breeding adults
founder effect
occurs when a population is established by a small number of individuals
genetic bottleneck
develops when a population undergoes a drastic reduction in size
fixation
when an allele has reached a frequency of 1, it has reached this
leads to a loss of genetic variation within a population
fitness
the reproductive success of a genotype compared with that of other genotypes in a population
selection coefficient (s)
the relative intensity of selection against a genotype
directional selection
one allele or trait is favored over another
Type 2 of natural selection is this
WAA=WAa < WAA
overdominance
also called heterozygote advantage
both alleles are favored in the heterozygote and neither allele is eliminated from the population
Type 5 of natural selection is this
WAA < WAa > Waa
underdominance
the heterozygote has lower fitness than either homozygote
leads to an unstable equilibrium
Type 6 of natural selection is this
WAA > WAa < Waa
evolution
genetic change taking place in a group of organisms
two step process: genetic variation arises and change in the frequencies of genetic variants
