Q15.3-2CC - Campbell Biology

Question

For each type of offspring of the test-cross in Figure 15.9, explain the relationship between its phenotype and the alleles contributed by the female parent. (It will be useful to draw out the chromosomes of each fly and follow alleles throughout the cross.)

Step-by-Step Solution

Answer

The female parent contributes the alleles, and the male parent contributes recessive alleles. The contribution made by the female parent determines the offspring's phenotype. 

Step 1: Description of offspring

Offspring is the young one of the organism. In sexual reproduction, the fusion of male and female gametes results in the formation of gametes. The offspring produced from sexual reproduction tends to possess the character of parents. 

Step 2: Description of the dominant and recessive allele

An allele is a variant present in the gene. The recessive allele is the allele that masks its effect. The other type of allele is the dominant alleles that get expressed in the offspring.

Step 3: Allelic expression in the phenotype

The phenotype of the test crossing produced offspring such as wild type (gray normal), black vestigial, gray vestigial, and black normal. Out of these offspring, only female characters are more prominently seen in these offspring. 

The male characters are recessive alleles, so the expression is not prominent. The alleles that are found in the eggs are exposed to the phenotype of the organism.

Hence, the female characters are predominantly seen in the test cross.