Morgan, in his dihybrid crosses with Drosophila observed deviations in the phenotypic ratio of F 2 progeny in comparison to that of Mendel. With the help of a suitable example, explain how his results deviated from that of Mendel.

Morgan carried out several dihybrid crosses in Drosophila melanogaster (fruit fly) to study genes that were sex-linked. The crosses were similar to the dihybrid crosses carried out by Mendel in peas. E.g. Morgan hybridised yellow bodied white-eyed female to brown bodied red-eyed male and intercrossed their F1 progeny. He observed that the two genes did not segregate independently of each other and F2 ratio deviated vary significantly from the 9:3:3: 1 ratio. Based on the cross Morgan stated that: (i) when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combination was much higher than the non-parental type. It is due to the linkage of two genes and the nonparental gene combination is described as recombination. (ii)when genes are grouped on the same chromosome, some genes were very tightly linked (low recombination) while others are loosely linked (high recombination). For eg. The genes white(w)and yellow(y) were tightly linked and showed 1.3% recombination while white(w) and miniature wing(m) showed 37.2% recombination.

E M B I B E

Xam Idea Biology>Chapter 5 - Principles of Inheritance and Variation>SELF-ASSESSMENT TEST>Q 12

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12th CBSE

IMPORTANT

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Why did T.H. Morgan select Drosophila melanogaster as a specimen for his experiments?

Important Questions on Principles of Inheritance and Variation

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12th CBSE

IMPORTANT

Xam Idea Biology>Chapter 5 - Principles of Inheritance and Variation>SELF-ASSESSMENT TEST>Q 12

Morgan, in his dihybrid crosses with Drosophila observed deviations in the phenotypic ratio of F₂ progeny in comparison to that of Mendel. With the help of a suitable example, explain how his results deviated from that of Mendel.

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