Answer:
A
The high frequency of achromatopsia in the Pingelap is attributed to the bottleneck and founder effects. Both of these are forms of genetic drift.
B
Blanks:
The relatively high frequency of the mutant achromatopsia allele in the island population is due to 3. genetic bottleneck created by the typhoon.
After the typhoon, the allele frequency was at least 7. 1/40, corresponding to one male 9. heterozygote among the 20 individuals surviving the storm.
The mutant achromatopsia alleles of the male, along with those of the other reproducing survivors, become 10. predominant in the expanding population.
Explanation:
A
Achromatopsia is a rare, autosomal recessive form of complete colour blindness. Usually, only 1 in 20,000 people are affected with achromatopsia. However, Pingelap, a cluster of islands in the Federated States of Micronesia, possesses disease rates as high as 10% of 3000 people. 30% of the 3000 are reported to be carriers of the achromatopsia allele. This unnaturally high allele frequency is linked to a genetic drift event that occurred after a typhoon killed majority of the population, leaving just 20 survivors. In terms of evolution, this is known as the bottleneck effect i.e. a severe reduction in a population due to natural disasters or sudden drastic environmental change. The bottleneck effect yields only a few viable individuals in the population.
Out of the 20 survivors, one is believed to be a carrier (heterozygous) for the achromatopsia allele. All of the achromatopsia affected Pingelapese trace their ancestry to one carrier. This is known as the founder affect where one or only a few individuals form or continue the population. This results in narrowing of the gene pool and drastic loss of genetic variations.
B
Blanks:
All the blanks have been explained above. Allele frequencies are calculated as follows:
