Evolution part 3

Question #4 If a certain trait's allele frequency is 100 percent, describe the genetic variation for that trait in the population.

If an allele frequency is 100% then there is no genetic variation for that trait.

Microevolution

Microevolution is the observable change in the allele frequencies of a population over time.

Gene flow

The movement of alleles from one population to another is called gene flow.

Question #2 Name two processes through which genetic drift can occur.

Bottleneck effect and founders effect

Question #3 How does sexual selection occur?

Certain male traits are favored by females when choosing a mate. Over time, the alleles associated with the preferred phenotype increase in the population.

Stabilizing selection

During stabilizing selection, the intermediate phenotype is favored and becomes more common in the population.

Question #1 How does gene flow affect neighboring populations?

Gene flow decreases genetic diversity between neighboring populations. (the populations will become more similar)

Genetic variation

Genetic variation is stored in a population's gene pool—the combined alleles of all of the individuals in a population.

Question #2 Describe two main sources of genetic variation.

Mutation: a random change in DNA that can result in a new allele. Recombination: rearranges allele combinations.

Genetic drift

Other alleles will likely increase in frequency and become fixed. These changes in allele frequencies that are due to chance are called genetic drift. Genetic drift causes a loss of genetic diversity in a population.

Question #3 How might the extinction of downy woodpeckers affect the phenotypic distribution of gall flies?

Selection could become directional in favor of medium-sized to large-sized

Question #4 How might overfishing of large pink salmon select for smaller body size in subsequent generations?

Smaller fish may be able to survive longer and reproduce more often than larger fish. Over generations, smaller adult salmon could become more common in the population. This is called directional selection.

Question #3 In what way is a gene pool representative of a population?

The gene pool contains all the alleles found in a population.

Normal distribution

This type of distribution, in which the frequency is highest near the mean value and decreases toward each extreme end of the range, is called a normal distribution.

Question #4 Would a population of 10 individuals or 100 individuals be more vulnerable to genetic drift? Why?

A smaller population is more vulnerable to genetic drift because it has a smaller gene pool and is therefore more likely to be affected by chance.

Directional selection

A type of selection that favors phenotypes at one extreme of a trait's range is called directional selection. Directional selection occurs when one extreme phenotype is favored by natural selection.

Question #2 What are the three ways in which natural selection can change a distribution of traits?

A.) directional selection: natural selection favors phenotypes at one extreme. B.) the distribution for these traits refers to the frequencies of the different phenotypes

allele frequency

An allele frequency is a measure of how common a certain allele is in the population.

Disruptive selection

Disruptive selection occurs when both extreme phenotypes are favored, while individuals with intermediate phenotypes are selected against by something in nature.

Question #1 Why does genetic variation increase the chance that some individuals in a population will survive?

Genetically diverse populations display high phenotypic variation. If changing environmental conditions favor a particular phenotype there is a good chance that genetically diverse population will have some individuals who have that advantageous phenotype.

Sexual selection

Sexual selection occurs when certain traits increase mating success. There are two types of sexual selection: • Intrasexual selection involves competition among males, such as the head- butting of bighorn sheep. Whoever wins the competition wins the female. • Intersexual selection occurs when males display certain traits that attract the female, such as peacocks fanning out their tails.

Bottleneck effect

The bottleneck effect is genetic drift that occurs after an event greatly reduces the size of a population. The bottleneck effect describes the effect of a destructive event that leaves only a few survivors in a population.

Question #1 In terms of phenotypes, describe what is meant by the phrase "distribution of traits."

The disruption for these traits refers to the frequencies of the different phenotypes.

Founders effect

the founder effect is genetic drift that occurs after a small number of individuals colonize a new area.