Final answer:
The high carrier frequency of the mutant G6PD allele is due to its role in providing resistance to Plasmodium falciparum malaria, which is beneficial in regions where the disease is endemic.
Step-by-step explanation:
The reason for the high carrier frequency of the mutant glucose-6-phosphate dehydrogenase (G6PD) allele is that it provides resistance against Plasmodium falciparum malaria. Mutations in the G6PD gene can lead to a form of anemia when inherited, but they also confer a protective role against malaria, which has been historically one of the most widespread deadly diseases among humans. Individuals who are homozygous for this mutation are less susceptible to malaria infection. This advantage would increase the fitness of individuals in regions where malaria is endemic because those carrying the mutation would have higher survival and reproductive success rates than those without it.
In areas like Southeast Asia, Africa, and South America, P. falciparum has evolved resistance to several anti-malarial drugs, including chloroquine, mefloquine, and sulfadoxine-pyrimethamine. The rapid evolution of P. falciparum in response to selective pressure from commonly used anti-malarial drugs highlights the importance of genetic traits like the mutant G6PD allele that provide natural resistance to malaria.