Bar is a dominant mutation on the Drosophila X-chromosome. A Bar male crossed to a wildtype...

Bar is a dominant mutation on the Drosophila X-chromosome. A Bar male crossed to a wildtype female giving the following results:

Bar females 998

wild type males 1021

wild type female 1

Remember: in Drosophila two X-chromosomes make a female fly and one X-chromosome makes a male; the Y is irrelevant. XXX is lethal.

Part I: What are the complete and exact genotypes of each parent and each type of offspring?

female parent:

male parent:

Bar female F1:

wild type male F1:

wild type female F1:

Part II: (a) What went wrong during meiosis, (b) in what fly, and (c) at exactly what stage of meiosis?

Solutions

Expert Solution

Answer :

Part I- Genotype of male parent is XB Y

Female parent- X+ X+

Bar female F1- X+XB

Wild type male F1- X+ Y

Wild type female F1- X+X+Y ( Exceptional)

Part II- (a)The exceptional F1 flies are the result of abnormal X chromosome behavior during the process of meiosis in the female parent. Usually, the X chromosomes in these females disjoin or segregate from each other during meiosis. However, sometimes they might fail to do so producing an egg with two X chromosomes or an egg with no X chromosome.

Fertilization of these abnormal eggs with normal sperm leads to an unusual number of chromosomes in their offsprings resulting in unexpected phenotypes.

(b) The female parent

gladiator answered 1 year ago

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