In sea bass, the appearance of lateral stripes and red eyes are produced by the

Question

In sea bass, the appearance of lateral stripes and red eyes are produced by the dominant alleles L and R, respectively, which are found at two independently assorting loci. At these loci, the genotype ll produces lateral spots, and the genotype rr produces yellow eye color. To determine the genotype of a lateral-striped, red-eyed male, a test-cross is performed. The offspring are 115 striped, red-eyed; 121 striped, yellow-eyed; 130 spotted, red-eyed; and 120 spotted, yellow-eyed. What is the most likely genotype of the father?

Explanation / Answer

A test cross is the one in which a F1 offspring is crossed with a homozygous recessive parent and following Mendelian pattern of inheritance of independent assortment, gives a final phenotypic ratio of 1:1:1:1. For this to happen, one of the parents should be homozygous recessive in nature and the other should be heterozygous at all allelic populations.

The quantitative information clearly suggests that the test cross offsprings are obtained as:

striped, red eyed: striped, yellow-eyed: spotted, red eyed: spotted yellow eyed :: 1:1:1:1.

This ratio clearly suggests that the population indeed follows Mendelian pattern of inheritance. Since this test cross ratio can be obtained only when one of the parents is homozygous recessive, it states that the genotype of the father is most likely to be spotted-yellow eyed or "llrr" in nature.

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