Crossing over occurs in Drosophila females, but it does not occur in Drosophila

Question

Crossing over occurs in Drosophila females, but it does not occur in Drosophila males. Genes a and b are separated by 10 map units on a Drosophila autosome.

If a+ b+/a b females are crossed to a+ b+/a b males, what percentage of the offspring will have.

1. the wild-type phenotype for a and also the wild-type phenotype for b? Enter your answer as a single number, rounded to one decimal place

2. the wild-type phenotype for a and the mutant phenotype for b?

3. the mutant phenotype for a and the wild-type phenotype for b?

4. the mutant phenotype for a and also the mutant phenotype for b?

Explanation / Answer

In crosing over , an arrangement in which the wild-type alleles of both loci are contributed by one parent is referred to as a cis configuration; the alternative arrangement is called a trans configuration. A gamete that shows the same configuration as the parent is referred to as a parental type; where the configuration is altered, the gamete is referred to as a recombinant type. Cis and trans configurations are altered by recombination.

Linkage between loci is indicated when the recombinant phenotypes occur less frequently than the parental types. The frequency of crossing over (% recombination) between two loci is directly related to the physical distance between those two loci. Percent recombination in a test cross equals map distance (1 map unit = 1 % recombination).

1. . the wild-type phenotype for a and also the wild-type phenotype for b?

Ans: 90%

2. The wild type phenotype for a and the mutant phenotype for b

Ans 10%

3.the mutant phenotype for a and the wild-type phenotype for b

Ans: 10%

4.the mutant phenotype for a and also the mutant phenotype for b

Ans: 10%

If           P1  --        a+b//a+b   x    ab+//ab+

              F1 --       a+b//ab+    x      ab//ab        (test cross)

             F2----    a+b//ab ,   ab+//ab   90% - parental combinations

                            a+b+//ab,   ab//ab 10% - recombinant

            10% recombinant indicates that loci a and b are 10 map units apart.

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.