Drosophila has four pairs of chromosomes: the sex chromosomes (XX in the females

Question

Drosophila has four pairs of chromosomes: the sex chromosomes (XX in the females; XY in the males) and three pairs of autosomes. You are studying a new mutant strain with blue eyes. You wish to know if blue eye colour is a dominant mutation and on which chromosome the blue eye locus can be found. When you cross a purebreeding female blueeyed fly with vestigial wings and spineless bristles to a male fly with wild type eye colour, wings, and bristles, all of the F1 progeny are completely wild type. An F1 male is backcrossed to a triple mutant female, producing the following progeny (remember that there is no crossing over in Drosophila males):

Wild type eyes, wings, and bristles:  72 females, 69 males

Wild type eyes and bristles, vestigial: 83 females, 77 males

Wild type wings, blue eyes, spineless:   60 females, 65 males

Blue eyes, spineless, vestigial:       62 females, 58 males

Is the mutation dominant or recessive?Explain.

Since you know that the locus for vestigial wings is on chromosome 2 and the locus for spineless bristles is on chromosome 3, what chromosome carries the locus for blue eyes? Show your work, including the stepbystep reasoning you used to arrive at your answer.

When an F1 female is backcrossed to a triple mutant male, the following 1,000 progeny are produced:

Wild type eyes, wings, and bristles:    90 females, 89 males

Wild type eyes and bristles, vestigial: 83 females, 98 males

Wild type eyes and wings, spineless: 37 females, 35 males

Wild type wings and bristles, blue eyes:   36 females, 34 males

Wild type wings, blue eyes, spineless: 92 females, 88 males

Wild type eyes, spineless, vestigial: 34 females, 39 males

Wild type bristles, vestigial, blue eyes: 33 females, 37 males

Blue eyes, spineless, vestigial:   90 females, 85 males

Calculate the map distance between blue eye and any linked genes. Show your work

Explanation / Answer

The mutation is a recessive mutation.. The following are the probable genotypes of the progeny after back crossing an F1 male to a triple mutant female.

(We is for wild eyes, Be is for blue eyes, Ww is for wild type wings, Vw is for vestigial wings, Wb is for wild type bristles, Sb is for spineless bristles)

The F1 generation should be heterozygous for the alleles with the genotype We Ww Wb/ Be Vw Sb

Since there is no crossing over, the males can produce the following gametes:

We Ww Wb and Be Vw Sb

1. We Ww Wb (M)

     Be Vw Sb (F)

2. Be Vw Sb (M)

    Be Vw Sb (F)

Only those progeny which have inherited  mutant gene from both parents expressed the trait. Also, all the F1 progeny had shown wild type. So, it is a recessive trait.

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