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Analyzing Protein Sequences

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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 - -

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Based 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.