17.2+-+Evo+as+genetic+change

Evolution as Genetic Change in Populations

__directional selection__: when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end __stabilizing selection__: when individuals near the center of the curve have higher fitness than individuals at either end __disruptive selection__: when individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve __genetic drift__: kind of __random__ change in allele frequency __bottleneck effect__: change in allele frequency following a dramatic reduction in the size of a population __founder effect__: situation in which allele frequencies change as a result of the migration of a small subgroup of a population __genetic equilibrium__: result of a population not evolving and allele frequencies not changing in a gene pool __Hardy-Weinberg principle__: states that allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change __sexual selection__: a way in which many species individuals select mates based on heritable traits, such a size, strength, or coloration directional/stabilizing/disruptive

17.2 Questions:

1) a) //How does natural selection affect a single-gene trait?// Natural selection on single-gene traits can lead to changes in allele frequencies and, thus, to changes in phenotype frequencies.

b) //Compare directional selection and disruptive selection.//

2) a) //Define genetic drift.// A random change in allele frequency caused by a series of chance occurrences that cause an allele to become more of less common in a population.

b) //How can the founder effect lead to changes in a gene pool?//

3) a) //What five conditions are necessary to maintain genetic equilibrium?//

b) //Why is genetic equilibrium uncommon in actual populations?//