15 .Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a

Question

15.Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a male having cinnabar eyes is crossed with a wild-type female, what percentage of the F1 males will have cinnabar eyes?
(a) 0% (b) 25% (c)50% (d) 75% (e) 100%

KEY. 15: B

19.Unattached earlobes is an autosomal dominant trait. What is the chance of getting a child with UNATTACHED earlobes when the father is Aa and the mother is Aa?

(a) 0% (b) 25 % (c) 50 % (d) 75% (e) 100%

KEY: 19:D

Please give a good explanation to your answer, will give a thumbs up, thank you. (visual learner)

Explanation / Answer

15. As given, cinnabar eyes is a sex linked recessive characteristic in fruit flies. We have a wild type female (XX) and an affected male, but it is not given which chromosome cinnabar eyes is associated with. If cinnabar eyes is associated with the X chromosome, none of the F1 males will inherit it as the only copy of X chromosome comes from the wild-type female. If cinnabar eyes is associated with the Y chromosome, all the males will inherit this as the single Y chromosome present comes from the affected male. 25% as an answer is simply not possible, depending on the associated chromosome it could be either 0 or 100%.

19. If we draw a Punnett square for a cross between Aa and Aa,

We see 3/4, or 75% of the progeny containing atleast one dominant allele required for unattached earlobes (AA, Aa, Aa). 25% of the progeny will have attached earlobes (aa)

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