Biodiversity chapter 19

Define what is meant by a population’s gene pool

A population’s gene pool includes all the alleles for all genes present in all individuals of that population

Genotype frequency

the proportion of a particular genotype in a population

Phenotype frequency

the proportion of individuals showing a particular trait

Allele frequency

the proportion of a specific allele among all alleles in the population

Discuss the significance of the Hardy–Weinberg principle as it relates to evolution and list the five conditions required for genetic equilibrium

The Hardy–Weinberg principle provides a mathematical model describing populations that are not evolving. If allele frequencies change, evolution is occurring

The five conditions for genetic equilibrium are:

Random mating, No mutations, large population size, No migration (gene flow), No natural selection

The Hardy–Weinberg equation is:

p^2+2pq+q^2=1 and p+q=1

p=

frequency of dominant allele

q=

frequency of recessive allele

Define microevolution

Microevolution is small generation-to-generation changes in allele or genotype frequencies within a population

microevolutionary forces

nonrandom mating, mutation, genetic drift (bottleneck, founder effect), gene flow, natural selection

Nonrandom mating

changes genotype frequencies, often increasing homozygosity

inbreeding

mating of individuals who are more closely related than if they had been chosen at random (inbred individuals may have lower fitness)

assortative mating

individuals select mates by their phenotypes

Mutation

introduces new alleles into a population (a change in DNA, source of genetic variation, only mutations in reproductive cells are inherited)

Genetic drift

random changes in allele frequencies, especially in small populations (decreases genetic variation with a population, but increases genetic differences among different populations)

bottleneck:

population rapidly and severely decreases due to disease, exploitation, or sudden environmental change (allele frequencies may differ from those preceding decline)

founder effect

a few individuals from a large population found a new colony

Gene flow

migration of breeding individuals between populations, with corresponding movement of alleles, increasing variation and reducing differences

Natural selection

increases the frequency of alleles that improve survival and reproduction (members of a population that are better adapted to the environment have greater fitness, leads to adaptive evolutionary change)

A mutation can be one of three things to the organism that inherits it: beneficial

(helps the organism in some way) --> adaptive

A mutation can be one of three things to the organism that inherits it: deleterious

(harms the organism in some way) --> maladaptive

A mutation can be one of three things to the organism that inherits it: neutral

(does not affect the organism) --> neutral

Stabilizing selection

favors average phenotypes and reduces extremes (narrows bell curve)

Directional selection

favors one extreme phenotype, shifting the population mean (During drought, large seeds are the primary food source; natural selection favors larger beaks)

Disruptive selection

favors both extremes and selects against intermediate phenotypes (very rare)

Genetic variation

introduced into a population by mutation, sexual reproduction contributes to genetic variation by recombining mutations in new ways, which may be expressed as new phenotypes

Genetic polymorphism

multiple alleles exist within a population

Balanced polymorphism

two or more alleles persist due to natural selection (e.g., heterozygote advantage, frequency dependent selection-Relative frequencies of left-pointing cichlids and right-pointing cichlids varied slightly)

Neutral variation

genetic differences that do not affect fitness 4(survival, reproduction, difficult to determine)

Geographic variation

genetic differences among the same species across different locations, often forming clines

cline

gradual change in a species phenotype and genotype through a series of geographically separate populations as a result of an environmental gradient