Question

The substitution of a T for an A in the protein coding sequence of the globin gene introduced a SNP. This SNP changed an amino acid resulting in sickle cell anemia. Unaffected individuals have the DNA sequence GAGGAG, a BseRI restriction enzyme site, in their gene generating two DNA fragments of 2 and 4 kb. The A to T substitution occurs within the BseR1 site thus inactivating the site (GTGGAG). Draw the RFLP gel including results for a carrier, as well as homozygous normal and affected individuals.

Answer 1

Sickle cell anemia refers to a recessive inheritance disorder, in which every individual carries two copies of a gene. In normal individuals, both the copies of the globin gene are normal, and they generate 2 and 4 kb fragments of DNA on digestion by BseR1. A patient with sickle cell anemia is homozygous for the recessive gene and exhibits a mutation in both the copies of a globin gene.

Therefore, BseR1 could not digest the globin gene and generate a single 6Kb fragment of DNA. In a patient acting as a carrier, one copy of a globin gene is mutated and the other is normal. As a consequence, BseR1 digestion generates 6kb of the fragment of DNA (mutated copy) and 4 and 2 kb from the normal copy of a gene.