Chapter 12 Vocabulary: The Forces of Evolutionary Change

Vocabulary flashcards covering key terms and concepts from Chapter 12: The Forces of Evolutionary Change (Natural Selection, Hardy-Weinberg, and related ideas).

Evolution

Evolution occurs when there are changes in heritable traits from generation to generation; over time this can lead to the development of different species.

Natural selection

The mechanism of evolution; individuals with traits best suited to their environment survive and reproduce more, shaping populations.

Variation

There must be different traits among individuals in a population.

Heritability

Variation must be heritable—genetic and able to be passed from parents to offspring.

Gene pool

The combination of all the genes (including alleles) present in a reproducing population or species.

Allele

A version of a gene; a variant form of a gene at a given locus.

Allele frequency

Number of copies of an allele divided by the total number of alleles for the same gene in the population.

Population

A group of interbreeding individuals of the same species in a given area.

Gene

A unit of heredity that codes for a trait.

Chromosome

A structure carrying genes; homologous pairs exist in organisms, carrying alleles for traits.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Dominant allele

An allele that masks the presence of a recessive allele in the phenotype.

Recessive allele

An allele whose effects are masked by a dominant allele in heterozygotes.

Genotype

The genetic makeup of an individual—the specific combination of alleles it carries.

Phenotype

The observable traits resulting from the genotype.

Fitness

An organism’s genetic contribution to the next generation.

Adaptation

Heritable features that provide a selective advantage by improving an organism’s ability to survive and reproduce.

Directiona​l selection

Favors one phenotype over another.

Disruptive selection

Favors extreme phenotypes; intermediate phenotypes are less fit.

Stabilizing selection

Favors intermediate phenotypes.

Hardy-Weinberg equilibrium

A state where allele frequencies do not change from generation to generation, when certain assumptions are met.

p (dominant allele frequency)

The frequency of the dominant allele in the population.

q (recessive allele frequency)

The frequency of the recessive allele in the population.

p^2

Frequency of homozygous dominant individuals in the next generation.

2pq

Frequency of heterozygous individuals in the next generation.

q^2

Frequency of homozygous recessive individuals in the next generation.

Random mating

Mating occurs at random, not influenced by genotype.

Mutation

A change in the DNA sequence; a source of new genetic variation.

Migration

Movement of alleles between populations (gene flow), changing allele frequencies.

Genetic drift

Random changes in allele frequencies, more pronounced in small populations; occurs regardless of selection.

Null hypothesis

Allele frequencies do not change from one generation to the next.

Evolution is not only possible—it is unavoidable

Evolution is an ongoing process; allele frequencies can change under natural forces.