Populations evolve for many reasons. Suppose there is a small population of birds that have either brown chest feathers or yellow chest feathers, and the allele for the brown feathers is dominant. The frequencies for the two alleles in the population are approximately equal. For each event or condition described below, answer the following questions. What mechanism? Identify whether the event is natural selection, genetic drift, or gene flow. Gene pool effect. Select the best description of how the allele frequencies change. A. Birds with yellow chest feathers attract more mates and leave more offspring. What mechanism is in work here? What is the effect on the gene pool? B. A hurricane kills many birds at random. What mechanism is in work here? What is the effect on the gene pool? C. A conservation group releases several new birds to the area, to repopulate the birds. The new birds are predominantly brown feathered. What mechanism is in work here? What is the effect on the gene pool?

A. Birds with yellow chest feathers attract more mates and leave more offspring.

Mechanism: The mechanism that is involved in this event is imply that of natural selection. In this event, birds with yellow chest feathers have a greater fitness they attract more mates and leave behind more offspring, as they are selected for by natural selection.

Effect on the gene pool: Since birds of yellow chest feathers have greater fitness, the frequency of yellow feather birds would increase, since more offspring with yellow chest feathers would be produced more than the other bird having the other feather color.

B. A hurricane kills many birds at random.

Mechanism: The mechanism that occurs in this event is simply that of genetic drift. Here, a random change has occurred, which can simply be referred to as the bottle neck effect. Following the disaster, the population size of the bird reduces thereby increasing the chance of allele frequency of the population to change. Genetic drift is occurs more in a small population.

Effect on the gene pool: Allele frequency would change, but not predictably. In other words, since individuals left are chosen by random, and no real idea of which traits would have the highest fitness after the event, we cannot really tell which the pattern of change the allele frequency would take, but we are certain there would be a change in allele frequency.

C. A conservation group releases several new birds to the area, to repopulate the birds. The new birds are predominantly brown feathered.

Mechanism: This event can be described as gene flow, as new members with mostly brown feather are introduced into the population which would eventually bring a change in the gene pool.

Effect on the gene pool: The frequency of brown feather allele will increase. Bearing in mind that the allele frequency of brown feather allele and yellow feather allele is approximately equal, an introduction of new set of birds having mostly brown feathers would definitely bring about a change in the gene pool, leading to more brown feather allele. Hence, frequency of brown feather allele will increase.