Question

The figure shows the experiment of T.H. Morgan on the linkage. If in cross-I, genes are tightly linked and in cross-II, genes are loosely linked then what will be the percentage of recombination produced in cross-I and cross-II respectively?

• A. 98.7% and 62.8%
• B. 1.3% and 37.2%
• C. 37.2% and 1.3%
• D. 62.8% and 98.7%

Answer 1

Answer: (B)

Morgan and his students have found that linked genes show varied recombinations, some being more tightly linked than others, (i) In Drosophila, the crossing of yellow bodied (y) and white-eyed (w) female with brown bodied (y⁺) red-eyed (w⁺) male-produced F₁ to be brown bodied and red-eyed females, while males were yellow bodied and white eyed. On intercrossing of F₁ progeny, Morgan observed that the two genes did not segregate independently of each other and, therefore, the F₂ ratio deviated significantly from expected 9: 3: 3: 1 ratio. He found that 98.7% to be of the parental type and only 1.3% recombinant type.
(ii) In a second cross of Drosophila between white-eyed and miniature winged (wwmm) female with wild type or red-eyed normal winged (w⁺m⁺) males, all the F₁ were found to be of wild type, i.e., red-eyed and normal winged in females, while it was white-eyed and miniature wings in males. An F₁ female fly was then test crossed with white-eyed and miniature winged male. 62.8% of the progeny was of parental types while 37.2% were recombinant types.