Question

Lab 10 Evolutionary Mechanisms Homework 

Definitions:

 1. List and define four evolutionary processes change allele frequencies in population. Provide one example for each process. Each example must be different from the ones taught in lecture and lab ppt.

 2. Write two equations of Hardy-Weinberg principles. Explain the meanings of p, q, p², q², 2pq.

 3. List five assumptions of Hardy-Weinberg principles.

 4. Based on the outcome of natural selection, describe four different modes of natural selection. Provide one example for each mode. Each example must be different from the ones taught in lecture and lab ppt

Answer 1

1.Microevolution is the change in allele frequencies that occurs over time within a population.This change is due to four different processes: mutation, selection (natural and artificial), gene flow and genetic drift. This change happens over a relatively short (in evolutionary terms) amount of time compared to the changes termed macroevolution.

Natural selection occurs when individuals with certain genotypes are more likely than individuals with other genotypes to survive and reproduce, and thus to pass on their alleles to the next generation.

Genetic drift results from the sampling error inherent in the transmission of gametes by individuals in a finite population. The gamete pool of a population in generation t is the total pool of eggs and sperm produced by the individuals in that generation.

Gene flow is the movement of genes into or out of a population. Such movement may be due to migration of individual organisms that reproduce in their new populations, or to the movement of gametes (e.g., as a consequence of pollen transfer among plants).

2.

Population Genetics and Evolution

Introduction

Key Concepts

• Concept 1: A Large Breeding Population
• Concept 2: Random Mating
• Concept 3: No Change in Allelic Frequency Due to Mutation
• Concept 4: No Immigration or Emigration
• Concept 5: No Natural Selection
• Concept 6: Estimating Allelic Frequency
• Concept 7: The Hardy-Weinberg Equation
• Concept 8: Sample Problem 1
• Concept 9: Sample Problem 2
• Concept 10: Sample Problem 3
• Concept 11: Allelic Frequency vs. Genotypic Frequency

Design of the Experiment

Analysis of Results

Lab Quiz

LabBench Activity

The Hardy-Weinberg Equation

To estimate the frequency of alleles in a population, we can use the Hardy-Weinberg equation. According to this equation:

p = the frequency of the dominant allele (represented here by A)
q = the frequency of the recessive allele (represented here by a)

For a population in genetic equilibrium:
p + q = 1.0 (The sum of the frequencies of both alleles is 100%.)

(p + q)² = 1

so
p² + 2pq + q² = 1

The three terms of this binomial expansion indicate the frequencies of the three genotypes:

p² = frequency of AA (homozygous dominant)
2pq = frequency of Aa (heterozygous)
q² = frequency of aa (homozygous recessive)

3.five basic Hardy-Weinberg assumptions: no mutation, random mating, no gene flow, infinite populationsize, and no selection

4.

Directional selection

Directional selectionDirectional Selection:
A type of selection that removes individuals from one end of a phenotypic distribution and thus causes a shift in the distribution. occurs when natural selection favors one extreme of continuous variation. Over time, the favored extreme will become more common and the other extreme will be less common or lost. If thicker-shelled oysters are more resistant to breakage than thinner-shelled oysters, crabs will be less able to prey upon them, and thicker-shelled oysters will be more likely to survive to reproduce.

Stabilizing selection

Stabilizing selectionStabilizing Selection:
A type of selection that removes individuals from both ends of a phenotypic distribution, thus maintaining the same distribution mean. occurs when natural selection favors the intermediate states of continuous variation. Over time, the intermediate states become more common and each extreme variation will become less common or lost.Continuing our oyster example, very light-colored or very dark-colored oysters might be more frequently preyed upon by shore birds, simply because they are more obvious on the oyster bar

Disruptive Selection:

A type of selection that removes individuals from the center of a phenotypic distribution and thus causes the distribution to become bimodal. occurs when natural selection favors both extremes of continuous variation. Over time, the two extreme variations will become more common and the intermediate states will be less common or lost. Disruptive selection can lead to two new species.

This might happen in shallow water among rocks. Light-colored oysters are more crypticCryptic Coloration:
Coloration that allows an organism to match its background and hence become less vulnerable to predation or recognition by prey. (less easy for a predator to see) because they match the rock color. Dark-colored oysters blend into the shadows cast by the rocks. In this case, intermediate-colored oysters would be most heavily preyed upon by the crabs, and very light and very dark oysters would survive to reproduce.

Kin selection

Kin selectionKin Selection:
A type of selection that involves altruistic behavior, e.g., the protection of offspring, in which a parent acts to preserve the gene pool of offspring at the expense of itself. occurs when natural selection favors a trait that benefits related members of a group. Altruistic behaviors are a result of kin selection, and are best illustrated by animals with complex social behaviors. Worker bees exhibit altruistic behavior by spending their lives serving the hive while never having an opportunity to reproduce on their own. In terms of simple fitness, the worker bee does not reproduce and therefore the traits that allow it to be a worker should be selected against. However, because all of the bees in the hive are close relatives, a worker bee's genes will be passed to the next generation indirectly through the queen. The queen is able to produce many more related offspring than the worker alone. As a result, servicing the queen to allow her to reproduce a larger number of offspring results in a higher fitness for the worker bee even though it never reproduces directly.