Question

Myoglobin is a heme-containing protein composed of a single polypeptide chain. It is capable of binding oxygen to its heme group. Hemoglobin is a heme-containing protein composed of four polypeptide chains, each chain being capable of binding oxygen to its own heme group.
Structural analysis has revealed the structure of the myoglobin protein to be nearly identical to the structure of the individual polypeptide chains of hemoglobin.
Scientists have compared the primary structure of both myoglobin and hemoglobin proteins from humans to those of other species as a way of tracing evolutionary relatedness. Examine the data table below.

Protein Sequence Differences Between Human and Other Species

	Myoglobin	Hemoglobin
Whales	25	17
Lampreys	64	125
Sharks	88	-
Horseshoe Crabs	-	-

Base on the data table and the information provided regarding the structures of the two molecules, which of the following statements is correct?

• A. The myoglobin gene arose from the partial duplication of the hemoglobin gene.
• B. The hemoglobin gene arose from the repeated duplication of the myoglobin gene.
• C. Myoglobin and hemoglobin are examples of convergent evolution.
• D. The nucleotide sequences for myoglobin and hemoglobin are nearly identical.

Answer 1

The correct option is A The myoglobin gene arose from the partial duplication of the hemoglobin gene.

Studies have shown that the key globin protein that is evolved for function in various aspect of oxygen metabolism arise from the same lineage of jawed vertebrates. It is found that there is a genetic duplication that takes place in the haemoglobin gene lineage that gives rise to a proto-alpha and beta globin genes which form the myoglobin too.

So, the correct option is 'The myoglobin gene arose from the partial duplication of the haemoglobin gene.'