Chapter 21 Flashcards
Microevolution
A change in allele frequencies in a population over generations.
Genetic Variation
Differences in the compositions of genes or other DNA sequences among individuals.
Neutral Variation
Differences that do not confer a selective advantage or disadvantage, caused by mutations in non-coding regions of DNA.
Gene Pool
All the alleles for all loci in a population.
Hardy-Weinberg Equilibrium
The state of a population in which mating is random and none of the mechanisms of evolution are acting.
Adaptive Evolution
A process in which traits that enhance survival or reproduction increase in frequency over time.
Genetic Drift
A process in which allele frequencies fluctuate unpredictably from one generation to the next. Reduces genetic variation through loss of alleles.
Founder Effect
When a few individuals become isolated from a larger population.
Bottleneck Effect
Results from a drastic reduction in population size due to a sudden environmental change. By chance, the resulting gene pool may not be reflective of the original population’s gene pool.
Gene Flow
The movement of alleles among populations. Alleles can be transferred through the movement of fertile individuals or gametes. Tends to reduce genetic variation among populations over time.
Relative Fitness
The contribution an individual makes to the gene pool of the next generation, relative to the contribution of other individuals.
Directional Selection
Occurs when conditions favor individuals at one end of the phenotypic range.
Disruptive Selection
Occurs when conditions favor individuals at both extremes of the phenotypic range.
Stabilizing Selection
Occurs when conditions favor intermediate variants and act against extreme phenotypes.
Balancing Selection
Occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population. (heterozygote advantage, frequency dependent selection)
Heterozygote Advantage
Occurs when heterozygotes have a higher fitness than do both homozygotes.
Frequency Dependent Selection
The fitness of a phenotype depends on how common it is in the population.
Sexual Selection
Natural selection for mating success.
Sexual Dimorphism
Marked differences between the sexes in secondary sexual characteristics.
