Question

A dominant, sex-linked disorder found in fruit flies is the result of a gene located on the X chromosome. If a male with the disorder is crossed with a female without the disorder, how would the offspring be affected?

All female offspring and none of the male offspring would have the disorder.

All offspring would have the disorder, regardless of gender.

None of the female offspring and all male offspring would have the disorder.

None of the offspring would have the disorder, regardless of gender.

Answer 1

Say X is the dominant X allele, x is the recessive X allele, and Y is just Y.

Our cross looks like this: XY // xx

If you draw out a Punnett square for this cross, you'll find your offspring genotypes are Xx (affected female), Xx (affected female), xY (unaffected male), xY (unaffected male). This means all female offspring, but no male offspring, will have the disorder. Answer is A.

Answer 2

@themathwiz @matt101 No, the Y chromosome does not determine sex in fruit flies, it only allows for the production of sperm. Sex is determined by the ratio of autosomes on the X chromsome.

Answer 3

@mrdoldum ?

Answer 4

@allopersonwhat @ganeshie8 @electrokid

Answer 5

@themathwiz Well, let's just leave it as what @matt101 said, thought the truth is it is not that simple because some XY "males" are sterile because maleness is not what we think of in fruit flies.

Answer 6

Okay

Answer 7

@themathwiz I thought about it and thought about how to describe it, but I don't think it is necessary for you unless you are taking a course on fruit fly genetics. Otherwise it is pretty much ignored.

Answer 8

Okay, thank you though for all your help

Answer 9

I hadn't even considered that @mrdoldum - learned something new today!