Chapter 16: Changing Allele Frequencies

Vocabulary practice flashcards covering Chapter 15: Changing Allele Frequencies, including microevolution, mechanisms altering Hardy-Weinberg equilibrium, types of selection, and clinical correlations.

Microevolution

A small genetic change due to allele frequencies within a population occurring over a short time period.

Macroevolution

Large-scale genetic changes in a population that take place over an extensive time period.

Five conditions that change allele frequencies

The five evolutionary forces that disrupt Hardy-Weinberg equilibrium: nonrandom mating, migration, genetic drift, mutation, and natural selection.

Positive assortative mating

A mating preference where individuals choose partners who have similar characteristics to themselves, such as a tall person selecting a tall mate.

Negative assortative mating

A mating preference where individuals choose partners with opposing characteristics, such as a tall person selecting a short mate.

Endogamy

An example of nonrandom mating involving marriage strictly within a specific community or shared group, regardless of direct biological relatedness.

Polygamy

A non-random mating pattern in which males have offspring with several females, contributing to higher frequencies of specific traits such as albinism among the Hopi Indians.

Migration (Gene flow)

The movement of individuals and their alleles into or out of a geographic area, altering genotype frequencies and increasing diversity within a population.

Cline

A graded geographic variation in individuals that directly corresponds to gradual, continuous changes in the environment, such as skin color variations matching UV light levels.

Genetic drift

Random, unpredictable fluctuations in allele frequencies between generations that occur by chance rather than health or fitness advantages, exerting the strongest effect in small populations.

Founder effect

A form of genetic drift that occurs when a small group voluntarily leaves a large population to establish a new colony, causing their alleles to be overrepresented and reducing overall genetic variation.

Population bottleneck

A drastic reduction in the size of a large, genetically diverse population caused by an external catastrophe, overhunting, or natural disaster, leaving limited survivors.

Mutation

A change in DNA sequence that acts as a continual source of genetic variation and represents the only evolutionary force of the five that creates new alleles in a gene pool.

Heterozygote advantage

A condition in which individuals heterozygous for a specific gene possess a reproductive survival advantage under certain environmental conditions over either homozygous genotype.

Natural selection

A primary evolutionary driving force through which individuals with advantageous variations survive and reproduce at higher rates over long time scales.

Fitness

An organism's high rate of reproductive success and genetic contribution to future generations based on its ability to survive and leave offspring.

Negative selection

A type of natural selection that acts to eliminate deleterious, harmful traits or alleles from a population.

Positive selection

A type of natural selection that acts to retain and perpetuate an advantageous trait within a population.

Directional selection

A mode of natural selection where phenotypes at one extreme end of a distribution are favored due to environmental changes, such as the increase in finch beak size during dry years.

Stabilizing selection

A mode of natural selection that acts against extreme phenotypes and selectively favors intermediate phenotypes, such as average human birth weight.

Disruptive selection

A mode of natural selection that favors both extreme phenotypes over intermediate ones, producing a bimodal distribution within the population.

Mutation-selection balance

An equilibrium point where the rate at which deleterious alleles are eliminated by natural selection precisely equals the rate at which they are produced by new mutations.

Balanced polymorphism

The ability of natural selection to maintain stable frequencies of at least two distinct phenotypes in a population because multiple selective forces act in opposing directions on the alleles.

Sickle cell balanced polymorphism

The maintenance of an autosomal recessive allele in a population because heterozygous carriers gain protection against malaria without developing full disease.

Hardy-Weinberg equilibrium equations

Mathematical conditions used to evaluate whether allele frequencies and genotypes are changing at equilibrium, defined by the formulas $p + q = 1$ and $p^2 + 2pq + q^2 = 1$.

Old Order Amish

A population founded in the 1700s by fewer than $200$ individuals seeking religious freedom, whose practice of endogamy illustrates the founder effect.

Ellis-van Creveld syndrome

An autosomal recessive disorder of bone growth causing dwarfism and polydactyly, identified in $43$ of $50$ global cases among the Old Order Amish tracing back to Mr. and Mrs. Samuel King.

Polydactyly

A physical condition characterized by having more than five fingers or toes, seen in individuals affected by Ehlers van Krebold syndrome.

Artificial selection

The controlled breeding of animals or crop plants by humans with the specific intent of perpetuating individuals with desirable phenotypes.

Lactase persistence

A positive selection adaptation following animal domestication, maintaining the continuous production of the lactase enzyme into adulthood as a selective advantage

Eugenics

A concept meaning 'good in birth,' coined in the late 1800s by Sir Francis Galton, aimed at applying genetic knowledge to improve human existence.

Positive eugenics

A eugenic strategy designed to encourage the breeding of individuals possessing traits deemed positive or advantageous for survival.

Negative eugenics

A eugenic strategy that attempts to restrict the reproduction of individuals deemed unfit or genetically inferior through measures like forced sterilization.

? mating is a type of non-random mating where the chosen mate is a relative

consanguineous

? mating is a type of non-random mating where the mate is chosen based on phenotypes

assortative mating

nonrandom mating alters ? frequencies, where it could be overrepresented, increased homozygotes, or reduced heterozygotes

allele

harmful recessive alleles are maintained in _ and are reintroduced by ?

heterozygotes

mutations

natural selection is the major force driving ? frequency change, transforming ?, and the force that shifts allele ? within large populations.

allele

populations

frequencies

could eugenics work to eliminate lethal alleles?

it could reduce it but cannot eliminate as it stays in heterozygotes thus it’s always maintained.