Chapter 20 - Evolution

species

a group of individuals that are capable, through reproduction, of sharing alleles with one another

gene pool

consists of all the alleles present in all of the individuals in the species

populations

interbreeding groups of organisms of the same species living in the same geographical area

two sources of genetic variation

mutation and recombination (shuffles mutations into new permutations)

somatic mutations

Mutations that occur in body cells, aren't passed to offspring, and don't affect the gametes

germ-line mutations

affect gametes; heritable and relevant to evolution

neutral mutation

a mutation that has no effect on survival or reproduction

deleterious mutation

Genetic changes that are harmful to an organism.

advantageous mutation

a mutation that increases chances of survival

allele frequencies

The proportion of a specified allele among all the alleles of a gene in a population

fixation

the change from a situation where there are at least two alleles to a situation where only one of the alleles remains

fixed population for a certain allele

population only exhibits one allele at a particular gene

genotype frequency

proportion of each genotype among individuals in the population at a particular gene/set of genes

three ways to measure genotype and allele frequencies in populations

1. observable traits

2. gel electrophoresis

3. DNA sequencing

Hardy-Weinberg principle

condition in which a population's allele frequencies for a given trait do not change from generation to generation

Hardy-Weinberg conditions

1. No mutations

2. Random mating

3. No natural selection

4. Extremely large population size

5. No gene flow

genetic drift

A change in the frequency of an allele due to the random effects of small population size

nonrandom mating

Mate selection biased by genotype or relatedness.

Hardy-Weinberg equation

p^2 + 2pq + q^2 = 1

p + q = 1

natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

evolution

A change in allele or genotype frequency in a population over time

fitness

a measure of the extent to which the individual's genotype is represented in the next generation

the modern synthesis

A comprehensive theory of evolution that incorporates genetics and includes most of Darwin's ideas, focusing on populations as the fundamental units of evolution.

intersexual selection

Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.

intrasexual selection

A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.

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

stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

directional selection

Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

artificial selection

selection by a breeder rather than by natural selection

heterozygote advantage

Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools.

inbreeding depression

when individuals with similar genotypes - typically relatives - breed with each other and produce offspring that have an impaired ability to survive and reproduce