Question 3b Suppose you discovered a female Drosophila melanogaster fly that was

Question

Question 3b

Suppose you discovered a female Drosophila melanogaster fly that was clearly smaller than
usual and had already been fertilized by at least one of the wild type males in the bottle. Youisolate the female and allow her to lay eggs. All of her first generation offspring are small like themother. Using this offspring as a starting point, design a set of experiments to help determinethe type of inheritance for the trait. Indicate what results would be expected in each generationfor each of the following types of inheritance:

(b) X-linked dominant inheritance of the small body phenotype.

Explanation / Answer

If all of the first generation offsprings are small, means small mutation is dominant over normal body size of the wild type. When only one allele is required to express a trait, as is this, its inheritance pattern is dominant. The genotype of a small body size fly could be Sb/+ or Sb/Sb.

In X linked dominant inheritance, all females and all males will be small, Female genotype will be XsbXsb or XsbX.

Males will have genotype XY (males are given in the above qs as wild type. So, they are normal sized, not small.) If XY male had been crossed with XsbX, then half of progeny in first generation should have been normal sized. But this is not the case. The entire first generation has been shown to be small, means that XY had been crossed with XsbXsb

so, inheritance pattern is X linked dominant.

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