Question

Human adult hemoglobin is a tetramer containing two alpha (α) and two beta (β) polypeptide chains. The α gene cluster on chromosome 16 and the β gene cluster on chromosome 11 share amino acid similarities such that 61 of the amino acids of the α-globin polypeptide (141 amino acids long) are shared in identical sequence with the β-globin polypeptide (146 amino acids long).

How might one explain the existence of two polypeptides with partially shared function and structure on two different chromosomes?

A. The clusters arose from the same ancestral gene.

B. Similar genes arose by random chance.

C. There is no explanation for the phenomenon yet.

Answer 1

Answer: A. The cluster arose from the same ancestral gene.

Explanation: In amniotes, i.e. mammals and birds, the coordinated regulation among gene clusters on different chromosomes and the differential expression of paralogous globin genes within the clusters is responsible for the existence of two polypeptides with partially shared function and structure on two different chromosomes. Such regulation and differential expression is possible because the clusters arose from the same ancestral gene.