Chapter 13, Problem 1VCQ

Figure 13.3 In a test cross for two characteristics such as the one shown here, can the predicted frequency of recombinant offspring be 60 percent? Why or why not?

Summary Introduction

To analyze:

If the predicted frequency of recombinant offspring can be 60 percent or not.

Introduction:

When a cross takes place between the dominant phenotype trait of an organism and a recessive phenotype trait (recessive homozygous genotype) is called a test cross. This is called a test cross because it helps to test the genotype (homozygous or heterozygous) of an organism.

Explanation of Solution

The organism having a dominant trait whose genotype is unknown is crossed with a homozygous recessive trait and then progeny is analyzed. The homozygous parent will produce only one type of gamete, but the heterozygous individuals will produce two types (in the case of monohybrid) and four types of gametes.

It has been found that any progeny with recessive phenotype predicts that heterozygous is the dominant trait; whereas, when the progeny shows all dominant, subsequently the dominant trait had the homozygous dominant trait. Therefore, in a test cross for two characteristics such as the one shown in the mentioned figure the predicted frequency of recombinant offspring will not be 60%. The predicted frequency of recombinant offspring ranges from 0% (for linked traits) to 50% (for unlinked traits).

Conclusion

Hence, it can be concluded that the predicted frequency of recombinant offspring will not be 60% because it ranges from 0-50% in a test cross for two traits like one referred in this figure.