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A cross is made between homozygous fruit flies that differ for eye color (the st gene) and body color (the e gene). The F1 double heterozygote is shown below using chromosome notation. st+ e / st e+ st = the recessive allele for scarlet eyes; st+ = the dominant wildtype allele for red eyes e = the recessive allele for ebony body; e+ is the dominant wildtype allele for gray body.Are the chromosomes shown in the genotype above in cis or trans configuration? Based on this notation, what were the genotypes and phenotypes of the two parents of the F1?

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Jean Keeling
Jean KeelingLv2
28 Sep 2019
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Related questions

Problem A. You cross two homozygous parents: RRYY (round yellow) and rryy (wrinkled green) to produce an F1 generation. Round seeds are dominant, yellow seeds are dominant. You cross two F1s to produce the F2 generation. In the F2 generation, you find an individual with round yellow seeds. You do a testcross to find out the genotype of this “mystery” dominant/dominant phenotype. In the offspring of the cross, you find 1?2 have round yellow seeds and 1?2 have wrinkled yellow seeds.
1. Based on these data what was the genotype of the mystery F2?

Problem B. You carry out a dihybrid cross between a red-flowered rose with long pollen grains (A1A1 LL) and a white-flowered rose with round pollen (A2A2 l l). The flower color gene (A) shows incomplete dominance, and long pollen is completely dominant to round pollen. The genes for these traits are on different chromosomes so assort independently
2. What would be the phenotypes of the F1 generation?
3. What fraction of the F2 generation is expected to have red flowers and long pollen? (As always when traits are independent, what rule can you apply to save time?)

Problem D. In the example of epistasis presented in class, the agouti allele in mice (A) codes for striped hairs and is dominant to the allele for all black hairs (a). A loss-of-function allele for the pigment gene (b) produces no pigment and is recessive to the normal, dominant allele (B). The recessive allele at b masks the effect of the A gene. A dihybrid cross of AABB and aabb is carried out.
5. Name all of the genotypes in the F2 generation that can produce an albino (no pigment) phenotype.

Problem E. A cross is made between homozygous fruit flies that differ for eye color (the st gene) and
body color (the e gene). The F1 double heterozygote is shown below using chromosome notation.
st+ e
--------------------------------------
st e+
st = the recessive allele for scarlet eyes; st+ = the dominant wildtype allele for red eyes e = the recessive allele for ebony body; e+ is the dominant wildtype allele for gray body

6. Are the chromosomes shown in the genotype above in cis or trans configuration?
7. Based on this notation, what were the genotypes and phenotypes of the two parents of the F1? (Think carefully here...)
8. With what phenotype would you cross this F1 to measure recombination frequency?

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.


The genes for sepia eye color, short bristles, and dark body coloration are on the same chromosome of Drosophila melanogaster. Each gene has two alleles: wild type, which is dominant, or mutant, which is recessive.

se+ is dominant and causes red eyes; se is recessive and causes sepia eyes

sb+ is dominant and causes long bristles; sb is recessive and causes short bristles

b+ is dominant and causes gray body coloration; b is recessive and causes dark body coloration

The sepia gene and short bristle gene are separated by 32 map units; the short bristlegene and the dark body gene are separated by 13 map units. The sepia gene and dark bodygene are separated by 45 map units.

If you crossed a fly, which was homozygous for the wild type allele of each gene with a homozygous recessive fly for each gene, the F1 generation would entirely consist of flies that had the wild type traits, but were heterozygous for each gene.

If you were to cross these heterozygous F1flies to recessive homozygous flies, how many flies would you predict to have the double cross-over phenotype? (You will show all of your work and phenotypic classes in the next problem. Just show the NUMBER of double cross-over flies predicted by the map unit data here. Round to a whole number)

If you were to cross these heterozygous F1flies to recessive homozygous flies, how many flies would you predict to observe in each of the eight predicted phenotypic categories with respect to these three genes (given the map units above) if there were 1,000 total offspring? Please show work and show all phenotypic classes!

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