Question

A person with a phenotype of HbSS has sickle cell disease. A person with a phenotype of HbAS allele carries the sickle cell trait. A person with a phenotype of HbAA does not have sickle cell disease and does not carry the trait. The Punnett square shows the phenotype of two people carrying the sickle cell trait. Hb A S A AA AS S AS SS What are the chances that their offspring will have sickle cell anemia?

Answer 1

The right answer is 1/4.

Two carriers of the disease each have a chance in two to transmit their sick gene ie: 1/2 * 1/2 = 1/4

A genetic disease is said to be autosomal recessive when

The gene involved is carried by an autosome (non-sex chromosome, X or Y in XY system of sexual determination);

The associated phenotype of this trait is recessive (the presence of two identical alleles is essential for the character to be expressed).

One of the two alleles is transmitted by the male gamete, the other by the female gamete.

But being a carrier of the mutation does not necessarily mean being sick, the manifestations of a genetic disease depend on its penetrance and the variability of its expression.