PROBLEM #2 Sickle-cell anemia is an interesting genetic disease. Normal ho ozygo

Question

PROBLEM #2 Sickle-cell anemia is an interesting genetic disease. Normal ho ozygo have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals us individials (SS) the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these "partially defective" red blood cells. Thus, heterozygotes tend to survive better than either of the homozygous conditions, if 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene? 8

Explanation / Answer

Ans. Since the population is heterozygous(Ss) for the sickle cell gene.

So the cross between Ss and Ss

P1 Ss x Ss

Gametes S, s x S, s

F1 SS, Ss, Ss, ss

We have given that 9% of the population is born with severe form of sickle cell anemia(ss).

The population born with heterozygous form of sickle cell anemia will be 18% because the heterozygous ratio in F1 population is 1/2 double the ratio of homozygous population.

And we know that in heterozygous conditions the malaria parasite cannot grow. So, the 18% population will be more resistant to malaria.

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