Chapter 18 - Evolution of Populations

"What are we getting on the quiz?" "ONE HUNDRED!!!!!!!!!!!!!!!!!!!!!!"

gene pool

all the genes, including all the different alleles for each gene, that are present in a population at any one time

allele frequency

the number of times that an allele occurs in a gene pool compared with the number of alleles in that pool for the same gene

single-gene trait

trait controlled by one gene that has two alleles

polygenic trait

trait controlled by two or more genes

directional selection

form of natural selection when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

stabilizing selection

form of natural selection in which individuals near the center of a distribution curve have higher fitness than individuals at either end of the curve

disruptive selection

form of natural selection in which individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle of the curve

genetic drift

random change in allele frequency caused by a series of chance occurrences that cause an allele to become more or less common in a population

bottleneck effect

a change in allele frequency following a dramatic reduction in the size of a population

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population

genetic equilibrium

situation in which allele frequencies in a population remain the same

hardy-weinberg priniciple

principle that states that allele frequencies in a population remain constant unless one or more factors cause those frequencies to change

sexual selection

when individuals select mates based on heritable traits

gene flow

the movement of genes into or out of a population

speciation

formation of a new species

reproductive isolation

separation of a species or population so that they no longer interbreed and evolve into two separate species

behavioral isolation

form of reproductive isolation in which two populations develop differences in courtship rituals or other behaviors that prevent them from breeding

geographic isolation

form of reproductive isolation in which two populations are separated by geographic barriers such as rivers, mountains, or bodies of water, leading to the formation of two separate subspecies

temporal isolation

form of reproductive isolation in which two or more species reproduce at different times

hox gene

a group of homeotic genes clustered together that determine the identity of body parts in animals. All Hox genes contain the homeobox DNA sequence.