Mammals Have a Family Between 500 and 1000 Genes That

question 37

Multiple Choice

Mammals have a family between 500 and 1000 genes that encode receptor proteins on the surface of odor-receptor neurons. If all mammals have these genes, why do some mammals have a better sense of smell than others do?

• A) Some of the genes actively transcribing receptor proteins in some species are completely absent in other species.
• B) Some of the genes may have been mutated and rendered inactive in some species but not in others.
• C) Some species, particularly humans, rely much less on odor detection for survival; thus, the genes have mutated to encode proteins that aid in other senses, such as sight.
• D) Some species of mammals have a larger set of "basic odors" than other species.

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Definitions:

Serum

The component of blood that remains after clotting has removed the blood cells and clotting proteins, containing antibodies and other proteins.

Formed Elements

Cells (i.e., red and white blood cells) and cell fragments (i.e., platelets) of blood.

Leukocytes

White blood cells that are part of the body's immune system, involved in protecting the body against both infectious disease and foreign invaders.

Erythrocytes

Red blood cells, which are responsible for carrying oxygen from the lungs to all parts of the body and returning carbon dioxide to the lungs for expulsion.