A person who is heterozygous for the cystic fibrosis allele moves to a small, is

Question

A person who is heterozygous for the cystic fibrosis allele moves to a small, isolated community where no one previously carried the allele. if the cystic fibrosis allele protects against tuberculosis the same way the sickle cell allele protects against malaria, what should happen to the frequency of the cystic fibrosis allele in the community over time and why?

a. the cystic fibrosis allele should disapear from the population, because a single individual with the allele is not enough to proliferate

b. the cystic fibrosis allele should increase to a relatively high frequency, because heterozygotes with the allele will be more likely to survive than others

c. the cystic fibrosis allele should become fixed in the population, due to genetic drift

d. the cystic fibrosis allele should either disappear or increase in frequency, depending on chance as well as one tuberculosis prevalence and death rate

Explanation / Answer

D. The cystic fibrosis allele should either disappear or increase in frequency, depending on chance as well as on tuberculosis prevalence and death rate.

The inheritance of recessive genes (disease causing) can remain prevalent if presence of two copies of an allele is disadvantageous and presence of one copy of the allele may be advantageous.

For example in case of sickle cell anaemia, two alleles may cause sickle cell anaemia but carrying one allele is advantageous in regions where malaria is common because this single copy of allele offers resistance against malaria. Thus, many people still carry the allele of sickle cell anaemia, as natural selection does not remove it; this is called “balanced polymorphism.” The trait disappears if there is no disease in the population.

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