Chapter 23 Flashcards
Population
a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
the smallest unit that can evolve
microevolution
change in allele frequencies in a population over generations
evolution on its smallest scale
difference between characters that vary discretely and continuously (quantitatively)
discrete characters are an either/or thing and are determined by a single gene locus
quantitative characters vary along a contiuum within a population and results from the influence of 2 or more genes on a single phenotypic character
Hardy-Weinberg Principle
why is it useful in describing the genetic structure of a nonevolving population?
fundamental theorem of population genetics
allele frequency will NOT change if…
1) no mutation
2) no natural selection or sexual selection
3) no migration
4) population is very large
5) no gene flow
with it, we can find the frequencies of alleles and genotypes and describe the gene pool of a nonevolving population
Geographic variation
results when two or more populations are separated by geography and develop different genetic compositions
Cline
a graded change in a character along a geographic axis
Gene pool
a count of all alleles present in a population
What does it mean to say an allele is fixed in a population?
an allele is considered fixed whenever there can be no variation to it because only one allele exists for a particular locus in a population
What 3 evolutionary mechanisms cause allele frequencies within a gene pool to change?
1) genetic drift (bottleneck effect, founder effect)
2) gene flow
3) natural/sexual selection
What is the only mechanism that consistently causes adaptive evolution?
natural selection
requires 2 things:
1) genetic variability - from mutation and sexual recombination, random
2) differential success of genotypes (=relative fitness) - variability reduced as certain genes are selected against, weeded out, non-random
Genetic drift
chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next (especially in small populations)
Relative fitness
the contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals
Three “modes” of natural selection
1) directional selection - moving mean
2) disruptive selection - selecting for two extremes
3) stabilizing selection - selecting for intermediate
Sexual selection
when individuals with certain inherited characteristics are more likely to find mates
sexual dimorphism
the difference between the two sexes in secondary sexual characteristics
