In a cross between a male and female, both heterozygous for sickle cell anaemia gene, what percentage of the progeny will be diseased?
- 100%
- 50%
- 75%
- 25%
Answer
(4) 25%
Solution
Sickle-cell anaemia is an autosomal recessive disorder; only HbS HbS individuals are diseased.
Parents: HbA HbS HbA HbS (both carriers)
⇒ Progeny: 1 HbA HbA : 2 HbA HbS : 1 HbS HbS
∴ Diseased progeny = 14 = 25\%
Answer: (4)