In Drosophila, females are XX, while males are XY. Yellow bodies are determined by an X-linked recessive mutation Xb, while the dominant wild-type allele XB produces brown bodies. A heterozygous female is cross with a brown-bodied male to produce the F1 generation. From the F1 generation, males and females are mated at random. What genotypes and phenotypes would be expected among the progeny in the F2, and in what proportions?

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Patrina SchowalterLv2

1 Aug 2019

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A dominant mutation B results in brown eyes rather than thewildtype red eyes in Drosophila. Genotypes BB and Bb therefore havebrown eyes, whereas genotype bb has red eyes. The mutation showscomplete penetrance and is located on one of the autosomes. Ageneticist carries out a cross of homozygous brown (BB) byhomozygous red (bb). The following questions pertain to crossesmade using the F1 progeny of this cross, all of which have theheterozygous genotype Bb.

a.The F1 male and female progeny are matedtogether to produce an F2 generation. From the F2 generation, alarge number of brown-eyed males, taken at random, are mixedtogether in a bottle containing homozygous bb females. Whatgenotypes and phenotypes would be expected among the progenyemerging from this bottle, and in what proportions?

b. The F1 male and female progeny are mated together to producean F2 generation. The brown-eyed F2 males and brown-eyed F2 femalesare mated at random. What genotypes and phenotypes would beexpected among the progeny, and in what proportions?

ochrefrog173

Genetics. A cross is made between two true-breeding parental strains in Drosophila. The following progeny data were obtained by scoring the males in the F2 generation:

white eyes/wildtype bodies: 6

wildtype eyes/ wildtype bodies: 492

white eyes/yellow bodies: 494

wildtype eyes/yellow bodies: 8

a) State the phenotypes of the F1 males and F1 females that produce the F2 progeny, assuming that both mutations are recessive.

b) Explain if white eyes are determined by a recessive allele of an X-linked gene.

c) Explain if wild type bodies are determined by a dominant allele of an X-linked gene.

d) Can the student conclude that the 2 genes assort independently? Explain.

e) If possible, calculate the recombination frequency for the two genes.

You are given 4 true-breeding mutant strains of fruit flies, each with a different eye colour
phenotype (apricot, orange, brown & scarlet). Specific reciprocal crosses between the recessive
mutant strains produced the following results in the F1 generations:
P1: apricot female x orange male F1 : apricot males and orange females
P1: orange female x apricot male F1 : orange males and females
P1: brown female x scarlet male F1 : wildtype males and females
P1: scarlet female x brown male F1 : wildtype males and females

i) Are the four mutant phenotypes all controlled by different alleles of a single gene? Explain.

ii) Which of the mutant phenotypes, if any, are due to allelic mutations?

iii) Which of the mutant phenotypes, if any, are due to alleles of autosomal genes? Explain.

iv) Using your own symbols for the mutations, indicate the genotypes of the F1 generation males
and females in each of the crosses.

v) Which of the F1 generations when intercrossed are likely to yield recombinant phenotypes in
the F2 generations? Explain showing the expected phenotypes and their proportions. (You
may assume that Mendelâs 2nd Law of Heredity holds true for the mutations involved in this
situation. Further assume that the double mutant results in a white eye color).

vi) Predict the outcome in the F1 generations of a reciprocal cross between a truebreeding strain
with brown eyes and another with apricot eyes.