Question

A population of endangered cheetahs has been suffering from a disease that causes malformation of the hips, resulting in the cheetahs having difficulty running to catch their prey. Conservation biologists want to devise a breeding program that they hope will get rid of the malformation in the population so that the population does not die out. They bring in four cheetahs from a different population that has never experienced this hip problem. When they breed the four outside cheetahs with four cheetahs who have the malformation, they find that none of the offspring have the hip problem.

a. What does this first round of breeding tell you about the dominance relationship between the normal hip (N) allele and the malformed hip (M) allele (assuming it is only this one allele that causes the malformation)? Explain how you determined this.

b. Should the conservation biologists conclude that the malformed hip allele is gone from the population? Why or why not?

c. What breeding should the conservation biologists do next to try to reduce or eliminate the M allele from the population? Why?

Answer 1

Answer a):

When allele that coded for normal hip (N) was introduced in the population from outside, the offspring of cross between (N) allele and malformed hip allele (M) gave all phenotypically normal hipped cheetahs. This clearly indicates that allele N is dominant over allele M.

Answer b):

The malformed allele M has not gone from the population but rather only subdued by the normal N allele. Hence, the population may phenotypically show normal hips, they still carry an malformed M allele within. This will reappear whenever offspring receives both recessive alleles, one from each parent. Hence the recessive allele is hidden genotypically due to presence of dominant N allele.

Answer c):

It is literally impossible to eliminate a recessive allele from a population for the simple reason that dominant alleles will hide the recessive alleles and even after 100 generations these might appear again as they are carried all along in the phenotypically normal population. More breeding from outside the population as was done for first normal generation will help. If pure breeds with both normal alleles come together more often they will help reduce the incidence od recessive allele but it is a known fact that a recessive allele can not be completely eliminated from a population. The natural selection phenomenon only sees the phenotypic appearance and does not consider a dominant homozygous individual any different from heterozygous individual that carries the recessive gene.