Biology 30 - Chapter 19

Population

any group of individuals of the same species living in the same geographical area at the same time

Gene

the basic unit of heredity; a specific sequence of DNA that encodes a protein, tRNA, rRNA molecule, or regulates the transcription of such a sequence; governs the expression of a particular trait and can be passed to an offspring

Allele

different form of the same gene occurring on homologous chromosomes

gene pool

total of all the alleles for all the genes of all the individuals in a population

genotype frequency

proportion of members of a population with a particular genotype; usually expressed as a decimal

phenotype frequency

proportion of members of a population with a particular phenotype; usually expressed as a decimal

allele frequency

rate of occurrence of a particular allele in a population, with respect to a particular gene; usually expressed as a decimal

Hardy-Weinberg principle

principle that states that allele and genotype frequencies remain constant from one generation to the next, as long as five conditions are met: (1) the population is large enough that chance events will not alter allele frequencies, (2) mates are chosen on a random basis, (3) there are no net mutations, (4) there is no migration, and (5) there is no natural selection against any of the phenotype

Hardy-Weinberg equation

mathematical description of the Hardy-Weinberg principle; used to predict allele and genotype frequencies in a population; usually stated

genetic equilibrium

condition of a gene pool in which allele frequencies remain constant over time; a population at genetic equilibrium is not changing or evolving; also known as Hardy-Weinberg equilibrium

Microevolution

gradual change in allele frequencies in a population over time

genetic diversity

degree of genetic variation within a species or population

Mutation

a permanent change in a cell’s DNA; includes changes in nucleotide sequence, alteration of gene position, gene loss, or duplication and insertion of foreign sequences; an inheritable mutation has the potential to affect an entire gene pool

gene flow

net movement of alleles from one population to another due to the migration of individuals and subsequent interbreeding

non-random mating

mating among individuals on the basis of mate selection for a particular phenotype or due to inbreeding, rather than mating on a random basis

genetic drift

change in allele frequencies due to chance events in a small breeding population; see also founder effect and bottleneck effect

founder effect

gene pool change that occurs when a few individuals start a new, isolated population; for example, on islands

bottleneck effect

gene pool change that results from a rapid decrease in population size

natural selection

process whereby the characteristics of a population of organisms change over time because individuals with certain heritable traits survive specific local environmental conditions and, through reproduction, pass on their traits to their offspring

heterozygote advantage

a survival benefit for those individuals who inherit two different alleles for the same trait (Aa), compared to those who are homozygous dominant or homozygous recessive; for example, the allele for cystic fibrosis may help carriers better resist diarrheal diseases such as cholera