Assertion [A]: Sickle cell anaemia affects only males.
Reason [R]: The mutation occurs at multiple regions in the gene responsible for sickle cell anaemia.

1. Both A and R are false
2. Both A and R are true and R is the correct explanation of A
3. A is true but R is false
4. Both A and R are true but R is not the correct explanation of A

The correct option is A Both A and R are false
Sickle-cell anaemia arises due to gene mutation in the autosomes and therefore can affect both males and females. If a mutated gene responsible for causing a disease is present in the Y chromosome, then it would affect only males.

Sickle-cell anaemia can be transmitted from parents to the offspring when both the parents are carriers for the gene or are suffering from the disease. Only homozygous individuals show the diseased phenotype.

The glutamic acid is replaced by valine at the 6th position of the beta haemoglobin chain. It is caused due to point mutation (substitution) at the sixth codon of the beta globin gene. The RBCs become sickle-shaped in affected individuals.
Hence, both A and R are false.