Ch. 23 Vocab

Evolution of Populations

microevolution

change in allele frequencies in a population over generations

genetic variation

caused by differences in genes or other DNA segments among individuals

phenotype

product of inherited genotype and environmental influences

introns

noncoding regions where most differences occur; 90% of the human genome

exons

coding regions that rarely change the amino acid sequence of the encoded protein; 10% of the human genome

mutation

a change in the nucleotide sequence of DNA

point mutation

change in a single nucleotide in a DNA sequence

Hardy-Weinberg equation

illustrates the genetic makeup one predicts for a population that is not evolving at a locus

neutral variation

variation showing no selective advantage or disadvantage

gene pool

aggregate of all copies of every type of allele at all loci in every individual in a population

population

localized group of individuals capable of interbreeding and producing fertile offspring

incomplete dominance

an inheritance pattern in which the heterozygous trait is a mix of the homozygous dominant and homozygous recessive traits

Hardy-Weinberg equilibrium

a population where gametes contribute to the next generation randomly and Mendelian inheritance occurs; allele and genotype frequencies remain constant from generation to generation 

Punnet Square

the way to confirm the frequency of genotypes without using an equation

phenylketonuria (PKU)

genetic disorder of a locus being in Hardy-Weinberg equilibrium

adaptive evolution

process in which traits that enhance survival or reproduction increase in frequency over time

genetic drift

describes how allele frequencies fluctuate unpredictably from one generation to the next; most pronounced in small populations; tends to reduce genetic variation through random loss of alleles

Founder effect

genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population

Bottleneck effect

when there is a major change in the gene pool due to a significant reduction in the population from human action or a disaster/change in environment

gene flow

the transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

directional selection

favors individuals at one extreme end of the phenotypic range

disruptive selection

favors individuals at both extremes of the phenotypic range

stabilizing selection

favors intermediate variants and acts against extreme phenotypes

sexual dimorphism

marked differences between the sexes in secondary sexual characteristics

intra-sexual selection

direct competition among individuals of one sex (often males) for mates of the opposite sex

inter-sexual selection

occurs when individuals of one sex (usually females) are choosy in selecting their mates; mate choice

good genes hypothesis

suggests that if a trait is related to male genetic quality, both the male trait and female preference for that trait should 

balancing selection

occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population

frequency-dependent selection

the fitness of a phenotype depends on how common it is in the population

heterozygote advantage

occurs when heterozygotes have a higher fitness than either homozygotes

sexual selection

Process in which individuals with certain inherited characteristics are more likely to acquire mates than other individuals of the same sex