17.2 Evolution as Genetic Change in Populations

Question 1

How does natural selection affect single-gene and polygenic traits?

Answer 1

Single-gene traits have natural selection cause changes in allele frequencies and thus, changes in phenotype frequencies.

Polygenic traits have natural selection cause changes to the relative fitness of some of the portions of phenotypes for a population.
Types of Natural Selection changes to these phenotypes include: Directional, Stabilizing, and Disruptive Selection

Question 2

What is Genetic Drift?

Answer 2

In small populations, individuals that carry a particular allele may leave more descendants than others by random chance. Over time, a series of chance occurrences can cause an allele to become more or less common in a population.
Examples also include bottlenecks, founder effect, and inbreeding which cause extinction vortexes.

Question 3

What conditions are required to maintain genetic equilibrium? (Hardy-Weinberg Conditions)

Answer 3

The Hardy-Weinberg principle predicts that five conditions can disturb genetic equilibrium and cause evolution to occur:

1) non-random mating (sexual selection to any degree)
2) Small population size (causing genetic drift to be a factor)
3) Immigration and Emigration (changes the “gene flow”)
4) Mutations (introduction of new alleles)
5) Natural Selection (different genotypes would have different levels of fitness and survival, thus causing evolution)

Question 4

Directional Selection

Answer 4

Type of natural selection acting on a polygenic trait when individuals at one end of the range of phenotypes have higher fitness than the other end.

Question 5

Stabilizing Selection

Answer 5

Type of natural selection acting on a polygenic trait when individuals near the center (intermediate) phenotype have higher fitness than the ones at either extreme (high or low)

Question 6

Disruptive Selection

Answer 6

Type of natural selection acting on a polygenic trait when individuals near the center (intermediate) phenotype have a lower fitness than the ones at either extreme (high or low)

Question 7

Bottleneck Effect

Answer 7

change in allele frequency following a dramatic reduction in population size (will usually reduce genetic diversity, depending on severity)

Question 8

Founder Effect

Answer 8

change in allele frequency as a result of a migration of a smaller subgroup from a population

Question 9

Genetic Equilibrium (Hardy-Weinberg Equilibrium)

Answer 9

If a population is not evolving, then the allele frequencies in its gene pool remain constant over time.

Question 10

Hardy-Weinberg Principle

Answer 10

states that allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change.

Question 11

Sexual Selection

Answer 11

act of selecting of mates based on heritable traits, such as size, coloration, or strength