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In Drosophila melanogaster, forked bristles are caused by an allele (Xf) that is X linked and recessive to an allele for normal bristles (X+). Brown eyes are caused by an allele (b) that is autosomal and recessive to an allele for red eyes (b+). A female fly that is homozygous for normal bristles and red eyes mates with a male fly that has forked bristles and brown eyes. The F1 are intercrossed to produce the F2. What will the phenotypes and proportions of the F2 flies be from this cross?

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Related questions

A cross is made between two true-breeding strains (P1generation) in Drosophila. The

following F2 data were obtained by intercrossing the F1 malesand females from this cross:

Phenotype # of flies

Claret eyes, wildtype bristles 255

Red eyes, frizzled bristles 248

Red eyes, wildtype bristles 497

Claret eyes, frizzled bristles 0

a) What were the phenotypes of the F1 males and F1 females thatwere crossed to produce the

F2 generation?

b) What were the genotypes of the F1 males and F1 females thatwere crossed to produce the F2

generation?

c) Explain whether a student can conclude that claret eyes aredetermined by a recessive allele of

an autosomal gene.

d) Can the student conclude that the 2 genes are syntenic (onthe same chromosome)? Explain.

e) Indicate the genotypes of the gametes that will be producedby the F1 males and females.

f) Illustrate, using appropriate symbols and convention, thegenotypes of the two true-breeding

parents of the F1 generation.

g) Predict the expected number of male and female flies in eachof the 4 phenotypes in a

population of 2000 flies, if the F1 male is crossed to a femalefrom a tester strain with claret

eyes and frizzled bristles.


3) In Drosophila, singed bristles (sn) and carnation eyes (car) are both caused by recessive, X-linked alleles. The wild-type alleles (sn+ and car+) are responsible for straight bristles and red eyes, respectively. A sn car female is mated to a sn+ car+ male and the F1 progeny are testcrossed. The F2 are distributed as follows

sn car

55

sn car+

45

sn+ car

45

sn+ car+

55

200

What is the value of X2 for a test of the hypothesis that the sn and car genes are unlinked?

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 pure-breeding female blue-eyed 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

a. Is the mutation dominant or recessive? Explain.

b. 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 step-by-step reasoning you used to arrive at your answer.

c. 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.

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