Question

There are many different breeds of dogs. The table below gives the average adult size of several of these breeds when individuals are raised in similar environments.

Breed Average Height (inches) Average Weight (pounds)
toy fox terrier 8.5 – 11.5 3.5 – 9.0
Pomeranian 7.0 – 12.0 4.2 – 7.7
Portuguese water dog 17.0 – 22.0 33.0 – 60.0
Irish wolfhound 32.0 – 35.0 115.0 – 180.0
Great Dane 28.0 – 34.0 99.0 – 200.0

Scientists identified a single gene that controls growth in dogs. They found that the Pomeranians and toy fox terriers have similar versions of this gene, but Portuguese water dogs, Irish wolfhounds, and Great Danes have different versions.

Which best explains the findings and the data in the table?
A.
The difference in size between Portuguese water dogs, Irish wolfhounds, and Great Danes produces different changes in the dogs' genes.
B.
The version of the gene in Pomeranians and toy fox terriers limits growth, so these breeds can only grow to small sizes.
C.
The environment in which the dogs grow changes their genetic material, and these changes affect the dogs' growth.
D.
The versions of the gene in Irish wolfhounds and Great Danes decrease the rate at which these breeds grow.
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Answer 1

B

Because the same gene variant is found in the two small breeds, that variant likely restricts growth (producing small adult size). The larger breeds have different gene versions that allow greater growth. Options A and C reverse cause and effect or invoke environment, and D describes a change (decreasing growth) that would not explain the large sizes.