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Biology · 2025 · 3 marks
CBSE 2025 · Region 4 · Set 2 · Q26
Thomas Hunt Morgan carried out several dihybrid crosses in Drosophila melanogaster to study genes that were sex linked. (a) Give four major reasons…
Thomas Hunt Morgan carried out several dihybrid crosses in Drosophila melanogaster to study genes that were sex linked.
(a)
Give four major reasons for using the tiny fruit flies by Morgan for his experiments.
(b)
How did Morgan and his group explain the physical association of the two genes on a chromosome to the frequency of recombination between gene pairs on the same chromosome ?
Marking-scheme solution
(a)
– Can be grown on simple synthetic medium in the laboratory
– Complete their life cycle in about two weeks / short life cycle
– Single mating could produce a large number of progeny
– There is a clear differentiation of the sexes/ the male and female flies are easily distinguishable/show sexual dimorphism
– It shows many heritable variations
– Inheritable variations can be observed under low power microscope easily
(b)
The tightly linked genes show very low recombination frequencies whereas, loosely linked genes show higher recombination frequencies
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