Question

A researcher identifies a mutation in rats he calls "zigzag" that causes the development of a bent tail in rats that are homozygous for the mutation. Heterozgyotes for the "zigzag" mutation have normal straight tails. A second mutation is identified by another researcher that she calls "crooked" that also causes a bent tail in rats that are homozygous for the mutation. Heterozygotes for the "crooked" mutation have normal straight tails. A true-breeding "zigzag" rat is crossed with a true breeding "crooked" rat. All their progeny have bent tails. This indicates that

A. the "zigzag" and "crooked" mutations are complementary.

B. the "zigzag" and "crooked" mutations are not complementary.

C. the "zigzag" and "crooked" mutations are alleles of the same gene.

D. A and C

E. B and C

Answer 1

The true-breeding "zig-zag" or tru-breeding "crooked" rats mean they pass on their traits to their offsprings and successive generations. This means they are homozygous for the traits.

.When a true-breeding "zigzag" rat is crossed with a true breeding "crooked" rat all the progeny have bent tails.

It is also given that some rats with homozygous "zig-zag" mutation alone and others with homozygous "crooked" mutation alone for the gene also have bent tails, when means either of the two mutations alone is sufficient to produce such trait in rats.

This means that:

• The "zig-zag" and "crooked" mutations are not complementary. (Since, complementary genes together produce a distinct qualitative effect from the one they produce alone.)
• The "zig-zag" and "crooked" mutations are alleles of the same gene.

Hence, the correct option is

E. B and C