Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Mutation is the process of alteration in DNA sequence when this alteration occurs in single base pair of DNA, this is known as point mutation and this change in single base pair is caused due to substitution or insertion/deletion of single base of DNA.
The well known example of point mutation is sickle cell anaema:
→ It is an autosomal recessive disorder which appears in offsprings only when both the parents are carrier of this gene.
→ This disease is caused due to a recessive gene Hb whereas its normal dominant allele is represented by Hb^s. In heterozygous (Hb^A Hb^s), exhibit sickle cell trait. Though heterozygotes are apparently unaffected as they carry atleast one normal gene allele. This is why heterozygous human can spend life normally doing work of less tireness but the homozygous humans for sickle cell (Hb^sHb^s) die in in childhood due to acute deficiency of normal RBCs as RBCs become non-functional.