25 terms

Chapter 17 Evolution of Populations

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gene pool
All the genes, including all the different alleles for each gene, that are present in a population at any one time
allele frequency
a measure of how common a certain allele is in the population
single-gene trait
trait controlled by a single gene that has two alleles
polygenic trait
trait controlled by two or more genes
p
the frequency of the dominate allele in a population
q
the frequency of the recessive allele in a population
2pq
the frequency of the heterozygous genotype in a population
q2
the frequency of the homozygous recessive genotype in a population.
p2
the frequency of the homozygous dominate genotype in a population
directional selection
occurs when natural selection favors one of the extreme variations of a trait
stabilizing selection
Natural selection that favors intermediate variants by acting against extreme phenotypes
disruptive selection
form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle
genetic drift
random change in allele frequencies that occurs in small populations
bottleneck effect
a reduction in the genetic diversity of a population caused by a reduction in its size
founder effect
genetic drift that occurs after a small number of individuals colonize a new area
genetic equilibrium
condition in which the frequency of alleles in a population remains the same over generations
Hardy-Weinberg Principle
principle that states that allele frequencies in a population remain constant unless one or more factors cause those frequencies to change
sexual selection
when individuals select mates based on heritable traits
species
A group of similar organisms that can breed and produce fertile offspring.
speciation
the formation of new and distinct species in the course of evolution.
reproductive isolation
separation of a species or population so that they no longer interbreed and evolve into two separate species
behavioral isolation
isolation between populations due to differences in courtship or mating behavior
geographic isolation
isolation between populations due to physical barriers which can lead to speciation
temporal isolation
form of reproductive isolation in which two populations reproduce at different times
molecular clock
Model that uses DNA comparisons to estimate the length of time that two species have been evolving independently