unit 7 set 4

Flashcards on Genetic Variation, Natural Selection, Speciation, and Evolutionary Patterns

Diploidy

Because most eukaryotes are diploid, recessive alleles are hidden from selection in heterozygotes.

Heterozygote advantage

Occurs when individuals who are heterozygous at a certain gene locus have an advantage for survival.

Reasons Natural Selection Doesn't Produce Perfect Organisms

Selection can only edit existing variations, evolution is limited by historical constraints, adaptations are often compromises, and chance interacts with natural selection and the environment.

Microevolution

Change in allelic frequencies of a population from generation to generation, confined to a single gene pool.

Macroevolution

Broad pattern of evolutionary change above the species level.

Biological species concept

A group of species whose members have the potential to interbreed in nature and produce viable, fertile offspring.

Reproductive isolation

The existence of biological barriers that prevent members of different species from producing viable, fertile hybrids.

Prezygotic barriers

Prevent mating or hinder fertilization if mating has occurred.

Types of prezygotic barriers

Habitat isolation, behavioral isolation, temporal isolation, mechanical isolation, and gametic isolation.

Postzygotic barriers

Prevent a hybrid zygote from developing into a viable, fertile adult.

Types of postzygotic barriers

Reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.

Allopatric speciation

A population forms a new species because it is geographically isolated from the parent population.

Sympatric speciation

A small part of a population forms a new species without being geographically separated from the parent population.

Adaptive radiation

Many new species arise from a single common ancestor, filling different ecological niches.

Gradualism

Species descend from a common ancestor and gradually diverge more and more in morphology as they acquire unique adaptations.

Punctuated equilibrium

Periods of apparent stasis punctuated by sudden change observed in the fossil record