Population Genetics and Evolution

Introduction

As early as the 500s B.C., several Greek philosophers theorized about the union of male and female traits to form offspring. In the 17th century, Leeuwenhoek concluded that semen and eggs carried hereditary factors conveyed to the offspring. Throughout the next century, scientists developed theories on the processes of development; LaMarck was one of the first to discuss the possibility of acquiring changed traits from parents. For example, he thought that if giraffes had to stretch to eat the tops of trees, their offspring would be born with longer necks.

Populations evolve by responding to their surroundings through natural selection. This change actually occurs in the frequency of gene alleles in the population. William Castle, an American scientist; Geoffrey Hardy, a British mathematician; and Wilhelm Weinberg, a German physician, independently determined that the frequencies of genes in a population remain constant unless certain forces act on the population. Dominant alleles will not replace recessive alleles, and the ratio of heterozygous and homozygous individuals does not change over the course of several generations. This theory has come to be known as the Hardy–Weinberg principle; it is the basis of the study of population genetics.

Objectives

In this experiment, you will

• Investigate a genetically inherited trait and apply the Hardy-Weinberg Principle to a population.
• Calculate allele frequencies and genotypes for a population using the Hardy-Weinberg formula.
• Compare allele frequencies within the classroom to North American averages.
• Demonstrate the stability of allele frequencies over five generations in an ideal Hardy-Weinberg population.
• Examine the effects of natural selection, heterozygous advantage, and genetic drift on allele frequencies in a simulated mating exercise.