Sickle cell anemia is a genetic disorder caused by a substitution mutation in the gene encoding hemoglobin, the protein on blood cells responsible for carrying oxygen. This mutation causes the hemoglobin protein to fold incorrectly, preventing the protein from carrying oxygen to the red blood cells.
Sickle cell anemia is inherited as a codominant trait, meaning that both alleles are expressed equally and that one is not dominant over the other. The allele for normal hemoglobin is represented by S, and the allele for abnormal hemoglobin is represented by s.
If two heterozygous individuals mate and produce offspring, what proportion of their offspring are expected to have fully sickled red blood cells?

The correct option is D 0.25

The cross can be represented as shown in the figure.

Sickle cell anaemia is a genetic disorder which is caused by a defective allele on chromosome. In homozygous condition, the disorder is lethal to the individual. In heterozygous condition, it leads to haemolytic anaemia under conditions of oxygen 60-70% deficiency.

Since the offspring with 'ss' genotype will have fully sickled red blood cells, their proportion will be:

no. of offspring with 'ss' genotype

-------------------------------------------------

Total no. of offspring

= 1/4

= 0.25

So, the correct answer is '0.25'.