Biology 16.2

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

1: List five conditions that can disrupt genetic equilibrium and cause evolution to occur

the first requirement is that allele frequencies not change overall because of mutations, the second requirement is that the population remain constant,the third requirement is the presence of a large population, the fourth requirement is random matings, and the fifth requirement is the absence of natural selection.

5:contrast stabilizing selection, disruptive selection and directional selection

1:Directional Selection occurs when selection favors one extreme trait value over the other extreme. This typically results in a change in the mean value of the trait under selection. 2:Disruptive Selection occurs when selection favors the extreme trait values over the intermediate trait values. In this case the variance increases as the population is divided into two distinct groups. Disruptive selection plays an important role in speciation. 3:Stabilizing Selection occurs when selection favors the intermediate trait value over the extreme values. Populations under this type of selection typically experience a decrease in the amount of additive genetic variation for the trait under selection.

genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

3:contrast gene flow with genetic drift

Gene flow happens when organisms move into or out of a population. That process brings in new genes to the gene pool or takes genes out of the gene pool. Genetic drift happens when a population gradually accumulates changes, becoming more and more adapted to the environmental conditions. So the population gradually becomes different than the way it used to be.

2: Explain the role of mutations in evolution

Mutations are the material upon which natural selection acts

directional selection

Natural selection in which individuals at one end of the phenotypic range survive and reproduce more successfully than do other individuals.

stabilizing selection

individuals with the average trait form of a trait have the highest fitness

emigration

is the movement of a population OUT of population

4:explain why the genetic drift is more significant in smaller populations

less mating possibilites because of smaller population

sexual selection

males are chosen with certain traits

immigration

movement of individuals INTO a population

gene flow

process of a gene moving from one population to another