1. Due to the role of Drosophila as a biological model, many eye color mutants h
ID: 9051 • Letter: 1
Question
1. Due to the role of Drosophila as a biological model, many eye color mutants have been isolated and used to analyze genetic control of eye pigmentation. Wild-type eye color is brick red due to a mixture of red and brown pigments. Vermillion (Xv) is a recessive, X-linked mutation causing bright red eye color due to lack of brown pigments. Brown (b) is a recessive, autosomal mutation causing brown eye color due to lack of red pigments. White eyes result from the loss of both red and brown pigments. Crosses between vermillion and brown flies show that the two mutations complement each other.a. What genotype(s) and eye color phenotype(s) do you expect to see in the progeny of a cross between a brown female and a vermillion male (both from true-breeding lines)? If male and female progeny would look different, clearly indicate this.
b. In a completely separate cross, half the progeny are brown-eyed and half the progeny are white-eyed. What are the genotypes and phenotypes of the parents?
Explanation / Answer
Part A)
according to the given informations:
wildtype = brick red eyes = red + brown
vermillion = red and lacks off brown; therefore to be vermilion individual must be either X^v X^v Bb or X^v Y B_
Brown = lacks of red and bb; therefore X^+ X^+ bb or X^+Y bb
white= lacks of both red and brown so X^+ X^v B_ or X^+ Y B_
we have:
female brown crosses with vermilion male
genotypes for them are:
female male
XX^+ X^+ bb X X^v Y B_(B or b) but it says that these guys are true breeding so! it is capital B
the cross will yield
female: X^v X^+ Bb red brick
male: X^+ Y Bb red brick also
Part B)
working backward from offspring to find out parents genotypes and phenotypes
we know half progeny are brown eyed and half the progeny are white eyed.
therefore
X^+ X^+ bb x X^+ Y Bb or X^+ X^+ Bb x X^+ Y bb i dont think it change anything. always, this lead to the parents must be:
X^+ X^+ bb (brown female) and X^+ Y Bb (white male) or X^+ X^+ Bb(white female) x X^+ Y bb (brown male)
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