AP Biology – Chapter 23 Vocabulary

Polymorphism- the coexistence of two or more distinct forms of individuals in the same population; occurs when two or more forms of a discrete character are evident in a population

Balanced Polymorphism- the ability of natural selection to maintain diversity in a population

Bottleneck Effect- a sudden change in environment (fire, flood) may drastically reduce the population size. Certain alleles may be overrepresented, underrepresented, or completely absent.

Founder Effect- a few individuals become isolated from larger population. This small group may establish a new population whose gene pool differs from source population.

Diploidy- organisms carry genes in pairs; recessive traits can be preserved in heterozygotes.

Frequency Dependent Selection- a decline in the reproductive success of a morph resulting from the morph’s phenotype becoming too common in a population

Gene Flow- the loss or gain of alleles from a population due to the migration of fertile individuals, or the transfer of gametes between populations

Gene Pool- all the genes present in a population at a given time

Genetic Drift- a change in a small population’s allelic frequencies due to chance

Genetic Structure- refers to any pattern in the genetic makeup of individuals within a population

Geographical Variation- differences in genetic structure between populations

Hardy-Weinberg Equilibrium- the frequencies of both alleles and genotypes will remain stable in a population; condition that describes a nonevolving population

Heterozygote Advantage- greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools

Hybrid Vigor- the improved or increased function of any biological quality in a hybrid offspring, the occurrence of a superior offspring from mixing the genetic contributions of its parents

Intrasexual Selection- a direct competition among individuals of one sex for mates of the opposite sex

Intersexual Selection- individuals of one sex are choosy in selecting their mates from individuals of the other sex, also called “mate choice”

Microevolution- a change in the gene pool of a population over a succession of generations

Morph- two or more forms of a discrete character

Natural Selection- differential success in the reproduction of different phenotypes resulting from the interactions of organisms with their environment

Population- localized group of individuals belonging to the same species

Species-group of populations whose individuals have the potential to interbreed and produce fertile offspring

Population Genetics- the study of genetic changes in populations

Relative Fitness- the contribution of one genotype to the next generation compared to that of alternative genotypes of the same locus

Sexual Dimorphism- the distinction between males and females on the basis of secondary sex characteristics

Directional Selection- natural selection that favors individuals at one end of the phenotypic range

Diversifying/Disruptive Selection-natural selection that favors extreme over intermediate phenotypes (each extreme is favored)

Stabilizing Selection- natural selection that favors intermediate variants by acting against extreme phenotypes