Question

3. You are part of a restoration ecology program that is attempting to reintroduce endangered European bison, Bison bonasus, into to suitable habitats in the Eurasia. This species went through an extreme bottleneck after they were almost wiped out during WWI. Maintaining what limited genetic diversity remains is an important priority, especially because diseases spread from cattle represent a major threat. A remote site for reintroduction has been identified in Belarus. Captive-bred bison destined for this site have been genotyped at a neutral marker locus "A" with two alleles, A 100 and A75. The genotype counts in the captive animals are as follows: A 100/A 100 -48, A 100/A75-24, and A75/A75-8 3a. If all of the bison are used to start the new population at the nature preserve, what is the probability that the population eventually becomes fixed for allele A75 through drift? 3b. Let's assume the population stays the same size (as the number of introduced individuals) in the new habitat. From this as the starting point, what would be the expected decline in heterozygosity over the next ten generations? 3e. In making decisions about reintroduction strategies, there might be a tradeoff in genetic diversity of founding populations (as measured by heterozygosity) and the total number of individuals introduced. Given the genotype counts of the captive bison from la, what is the largest population you could introduce with a starting heterozygosity of 0.5? 3d, Run this new H-0.5 (from 3e) starting population through the assumptions in 3b (with the population staying the same size as the new number introduced). What is the expected decline in heterozygosity for this population over ten generations?

Answer 1

You have asked multiple questions here. As per Chegg Q&A Guidelines, I am answering the first two questions.

The bison population has undergone genetic drift, which means that a random population got selected without any necessity of survival advantage while the rest of the population got wiped out. In the surviving population, a neutral marker locus was selected. This means that the allele present at the locus will not give any survival advantage.

Now this gene A has two alleles A100 and A75. The genotypic counts of the animals are:

A100/A100 = 48, A100/A75 = 24 and A75/A75 = 8.

Thus, the total number of animals that have survived = 48+24+8 = 80.

Therefore, the frequency of A100/A100 = 48/80 = 0.6

Frequency of A100/A75 = 24/80 = 0.3 and

Frequency of A75/A75 = 8/80 = 0.1.

a) Since the allele is neutral, if the allele A75 has to undergo fixation, which means that the allele A100 has to get wiped out, it would take infinite time. And the probability of this event would be the same as the probability of finding the allele A75 in the original population.

The number of alleles A75 = 24/2 + 8 = 12 + 8 = 20

Hence the frequency of this allele = 20 / 160 = 0.125 = 12.5%.

b) The expected heterozygosity after X generations for a population of size N that underwent a bottleneck is given by:

$[1-\frac{1}{2N}]^X$

In our case, N = 80 and X = 10.

.:: [1 - Jan 10 = [1 - 210 = [1 – 0.00625) 10 = 0.9937510 = 0.9392

That is we would expect 93.92% heterozygosity maintained as of the original population or a loss of approximately 7% heterozygosity.