CHAPTER 11 NOTESBiology

GENETIC VARIATION

Gene pool- the combined alleles of all the individuals in a population

Allele frequency- a measure of how common a certain allele is in the population

NORMAL DISTRIBUTION

Phenotypes near the middle of the range tend to be more common, while the extremes are less common.

DIRECTIONAL SELECTION

A type of selection that favors phenotypes at one extreme of a trait’s range.

Ex: low drug resistant bacteria to high drug resistant bacteria

STABILIZING SELECTION

The intermediate phenotype is favored and becomes more common in the population.

Ex: wasps feed on small gall flies and woodpeckers feed on large gall flies

DISRUPTIVE SELECTION

When both extreme phenotypes are favored by selection

Ex: blue- blue brown- dull brown lazuli buntings

Blue is dominant and see the other blue & blue brown as threats, leave the dull brown alone

MECHANISMS OF EVOLUTION

Gene flow- the movement of alleles from one population to another

Genetic drift- changes in allele frequency that are due to chance

BOTTLENECK EFFECT

Genetic drift that occurs after an event greatly reduces the size of a population

Ex: over hunting

FOUNDER EFFECT

Genetic drift that occurs after a small number of individuals colonize a new area.

Ex: dwarfism in old order Amish communities

SPECIATION THROUGH ISOLATION

Reproductive isolation occurs when members of different populations can no longer mate successfully with one another.

Speciation is the rise of two or more species from one existing species

BEHAVIORAL ISOLATION

Courtship dances, chemical scents, and courtship songs are signals for mating between populations

Behavioral isolation is caused by differences in these behaviors

OTHER ISOLATIONS

CONVERGENT EVOLUTION

Different species often must adapt to similar environments. Evolution toward similar characteristics in unrelated species is called convergent evolution.

DIVERGENT EVOLUTION

When closely related species evolve in different directions.

PUNCTUATED EQUILIBRIUM

Episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolutionary changes