chapter 18 college biology

evolution

The gradual change in a species over time

adaption

inherited characteristic that increases an organism's chance to survive and reproduce

population

a group of organisms of the same species populating a given area

Dimorphism

a trait that exists in only two forms in a population

polymorphism

The coexistence of two or more distinct forms in the same population.

gene pool

the sum of all the genes in the entire population

alleles

Different forms of a gene

phenotype

An organism's physical appearance, or visible traits.

gene mutation

heritable changes in DNA that can alter gene expression

lethal mutation

expression of a gene that results in death

neutral mutation

genes, whether or not they are expressed in the phenotype, have no effect on survival and reproduction

allele frequencies

a measure of the abundance of each kind of allele in the entire population

genetic equilibrium

situation in which allele frequencies remain constant

(1) no mutations occurring

(2) the population is very, very large

(3) the population is isolated from other populations of the same species

(4) all members survive, rate, and reproduce- no selection

(5) mating is random

microevolution

the change in allele frequencies brought about by mutation, genetic drift, flow, and natural selection

Hardy-Weinberg equilibrium equation

p^2 + 2pq + q^2 = 1 (p and q are allelic frequencies)

directional selection

shifts alleles in a consistent direction

antibiotic

destroys bacteria

stabalizing selection

favors the most common phenotype in a population; counters the effects of mutation, genetic drift, and gene flow

disruptive selection

favors forms of the extremes of the phenotypic range of variation and selects against the intermediate forms

sexual dimorphism

distinctive male and female phenotypes

sexual selection

when individuals select mates based on heritable traits; females are often the agents of selection when they pick their mates

genetic drift

random change in allele frequencies that is more significant in small populations, due to chance occurrences alone

Probability

the chance that something will happen relative to the number of times it could happen

fixation

one kind of allele remains at a specified locus in a population

bottleneck

process in which a large population declines in number, then rebounds; some stressful situation greatly reduces the size of a population, leaving a few (typical or atypical) individuals to reestablish the population

founder effect

a few individuals (carrying genes that may/may not be typical of the whole population) leave the original population to establish a new one

Inbreeding

nonrandom mating among closely related individuals

emigration

moving out of a population

immigration

Moving into a population

gene flow

movement of alleles from one population to another