Question

The Kermode Spirit bear is an alternate phenotype of the species Ursus americanus (black bear) in British Columbia that has striking white fur. It was determined in 2001 that a single nucleotide change from G to A results in the replacement of Tyrosine with Cysteine at codon 289 in the melanocortin 1 receptor gene (mc1r; Ritland et al. 2001 Current Biology). This allele (W2) is recessive to the wildtype allele (W1), and occurs as a novel mutation in 1 out of every 10,000 copies. White phenotypes range in frequency from 10% to 25% on various islands, and have been present for long periods of time. Each island has approximately 50 individuals. It has been estimated that the white bears have a 20% advantage over black bears in fishing salmon from rivers due to decreased contrast with the sky. Assuming these populations started out initially as 100% W1W1 (AA)

A. What evolutionary force(s) is/are acting on the W2 allele? Natural selection, mutation

B. If selection, mutation, and drift were the only processes acting on these populations, what would be the eventual outcome(s) for the two alleles in a given population?

C. Try running the simulation for fewer generations. How many generations does it take to fix a novel advantageous allele in all populations? What do these results suggest about the ability of selection to fix a novel advantageous mutation in a small population; in other words, why is selection "having trouble"?

D. Name one of the parameters you could change to increase the probability of the W2 allele becoming fixed in the population?

The questions are based on a graphing program called PopG

Answer 1

1. If the population started with W1W1 ( black bear ) then by natural selection W2W2 can't be formed because W2 allele is completely absent. By mutation there is a chance of creating new var iation in the population by changing in the base nucleotide sequence.

2. According to my opinion , if selection , mutation and drift were the only processes then the new population would be mostly white. That is, the chance of getting homozygous black bear is highly reduced, next to it the chance of heterozygous black bear ( chance greater than W1W1), and more chance for the white bears (W2W2).

3. According to my opinion it is really difficult to fix the novel advantages allele in all population. If all the new population were the advantages type, and if a sudden genetic drift happens then it can cause the entire vanishing of the species from the earth.

4. Genetic drift must remain constant , simply , the population must be obeying Hardy Weinberg law.