Question

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DIAGRAM the cross and determine which allele is dominant for each of the following Drosophilamatings:

a. Two red-eyed flies yield 110 red-eyed and 35 brown-eyed offspring.

b. A dark-bodied fly and a tan-bodied fly yield 76 tan and 80 dark offspring.

Answer 1

Ans.a The above case is an example of a monohybrid cross. In this case the red eyed flies are the dominant ones whereas the brown eyed are the recessive ones. Consider the case where R represents the red eyed flies dominant gene and b represents the brown eyed ones.

RR	Rb
Rb	bb

The above given trait shows that the trait follows a 3:1 ratio where the dominant gene expresses itself and the recessive ones are supressed. Hence the red eyed are the ones with the dominant trait.

Ans b. In the given case two dominant genes are crossed hence both of them has been expressed in the final trait.