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Antifreeze in Fish

APBIO-EVNJJ3

The Arctic cod is a species of fish found living in waters that reach below freezing temperatures. The fish are able to survive in subfreezing waters without their own cells freezing because they can produce an antifreeze protein that prevents the formation of ice crystals in the cytoplasm.

The DNA sequence that codes for the antifreeze protein is right next to the DNA sequence that codes for a digestive protein. A small intron sequence separates the two.

Based on this information, which of the following is MOST likely true?

A

The DNA sequence for the digestive protein and the DNA sequence for the antifreeze protein are linked genes.

B

The antifreeze sequence originated from the duplication of the existing DNA sequence for the digestive protein.

C

The digestive protein sequence originated from the duplication of the existing DNA sequence for the antifreeze protein.

D

A mutation in a third gene affects the expression of the two sequences so that their proteins products are different.