Question

A breeder wants to set up a program to produce zebrafish with long fins. Having long fins is a dominant trait compared to the short-finned wild type. Before she can market her zebrafish, she needs to perform a test cross on the long-finned fish she plans to use as a breeder. How can she tell whether her fish are homozygous or heterozygous for the long-finned trait? A. Cross the long-finned fish with short-finned fsh; if three-fourths of the offspring are long-finned and one-fourth are short-finned,the long-finned parent is homozygous. B. Cross the long-finned fish with short-finned fish; if three-fifth of the offspring are long-finned and one-fourth are short-finned,the long-finned parent is homozygous. C. Do several test crosses between the long-finned fish and short-finned fish; if the offspring are always long-finned, the long-finned parent is probably homozygous.

Answer 1

Answer:

Option C

Explanation:

Let the allele for long fin trait be "L" and the allele for short fin trait be "l"

Given L is dominant over l

If he crosses a long fish and short fin to produce three fourth long fins and one fourth short fins, it is not confirmed that the long fin species are homozygous as represented in the cross below

Ll * Ll

LL, Ll. Ll, ll

The two parent species are long (but not homozygous). Hence, option A is incorrect

However, if this test cross is carried out several times, the recessive trait may disappear thereby producing only homozygous long finned species.

Hence, option C is correct