Question

Sickle-cell anemia is an autosomal recessive disease, people with the disease have a ss genotype and people without the disease have a SS genotype. People who have the disease get very ill, but people who have only one copy of the recessive gene are actually protected from getting malaria (Ss heterozygote genotype). Which area of the world is the frequency of sickle cell anemia the highest? Why do you think this is true (related to heterozygote advantage)?

We talked about the disease hemophilia in reference to Sally. Based on what we know from the transmission pattern of the disease hemophilia (sex-linked recessive), why do you think it affects males more often than females?

Answer 1

the frequency of sickle cell anemia :

Sickle cell disease (SCD) affects millions of people worldwide.  But it is common among those whose ancestors came from Africa; Mediterranean countries ; Arabian peninsula India;Spanish-speaking countries (South America, the Caribbean, and Central America).

United states : 70000 to 80000 Americans are affected,

                          1 in every 500 African Americans

                           1 in 1000 to 1400 Hispanic Americans.

                           1 in 13 Black or African-American babies is born with sickle cell trait (SCT).

It is common in the countries where malaria is common. It is believed that people who carry the sickle cell triat are less likely to vave severe forms of malaria.

heterozygote advantage.

When a single copy of a disease allele it doesn't result in a disease but instead is good for the person or organism that carries it, this allele has a heterozygote advantage.

A heterozygote advantage describes that the case in which the heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype.

Hemophilia

Males are more often affected than females, because the gene is located on the X chromosome. Hemophilia A is a disorder where the blood cannot clot properly due to a deficiency of a clotting factor called Factor VIII. However, not all female carriers present these symptoms.

A female with one affected X chromosome is a “carrier” of hemophilia

But males can have a disease like hemophilia if they inherit an affected X chromosome that has a mutation in either the factor VIII or factor IX gene