Question

In Drosophila, gray body color is dominant over ebony body color, while long wings are dominant over vestigial wings. Work the following crosses through the \(F_{2}\) generation, and determine the genotypic and phenotypic ratios for each generation. Assume that the \(P_{1}\) individuals are homozygous: (a) gray, long \(\times\) ebony, vestigial, and (b) gray, vestigial \(\times\) ebony, long, and (c) gray, long \(\times\) gray, vestigial.

Short answer

Answer: - Part a: 9/16 Gray body, long wings; 3/16 Gray body, vestigial wings; 3/16 Ebony body, long wings; 1/16 Ebony body, vestigial wings - Part b: 9/16 Gray body, long wings; 3/16 Gray body, vestigial wings; 3/16 Ebony body, long wings; 1/16 Ebony body, vestigial wings - Part c: 2/4 Gray body, long wings; 2/4 Gray body, vestigial wings

Step-by-step solution

Determine the Genotypes of the Parents

For the gray, long parent, we have homozygous dominant alleles for both body color and wing length so the genotype is GGWW. For the ebony, vestigial parent, we have homozygous recessive alleles for both body color and wing length, so the genotype is ggww.

Determine the \(F_{1}\) Generation Genotypes and Phenotypes

Since the parents are homozygous, all the offspring will have one dominant allele and one recessive allele for each trait, resulting in a genotype of GgWw. The phenotypes for all \(F_{1}\) offspring will be gray body color and long wings.

Determine the \(F_{2}\) Generation Genotypes by Crossing \(F_{1}\) Offspring

To determine the \(F_{2}\) genotypes, we perform a dihybrid cross of two F1 individuals with genotypes GgWw. This will result in the following genotypes in the offspring: - 9/16: GGWW, GGWw, GgWW, GgWw (gray body, long wings) - 3/16: GGww, Ggww (gray body, vestigial wings) - 3/16: ggWW, ggWw (ebony body, long wings) - 1/16: ggww (ebony body, vestigial wings)

Determine the \(F_{2}\) Generation Phenotype Ratios

From the genotypes found in step 3, we can determine the phenotypic ratios of the \(F_{2}\) generation offspring: - 9/16: Gray body, long wings - 3/16: Gray body, vestigial wings - 3/16: Ebony body, long wings - 1/16: Ebony body, vestigial wings #Part b: Gray, vestigial x Ebony, long#

Determine the Genotypes of the Parents

For the gray, vestigial parent, we have homozygous dominant alleles for body color and homozygous recessive alleles for wing length, so the genotype is GGww. For the ebony, long parent, we have homozygous recessive alleles for body color and homozygous dominant alleles for wing length, so the genotype is ggWW.

Determine the \(F_{1}\) Generation Genotypes and Phenotypes

Since the parents are homozygous, all the offspring will have one dominant allele and one recessive allele for each trait, resulting in a genotype of GgWw. The phenotypes for all \(F_{1}\) offspring will be gray body color and long wings.

Determine the \(F_{2}\) Generation Genotypes by Crossing \(F_{1}\) Offspring

This cross is identical to the one in Part a, Step 3, and will result in the same genotypic ratios.

Determine the \(F_{2}\) Generation Phenotype Ratios

The phenotypic ratios will be the same as in Part a, Step 4. #Part c: Gray, long x Gray, vestigial#

Determine the Genotypes of the Parents

For the gray, long parent, we have homozygous dominant alleles for both body color and wing length, so the genotype is GGWW. For the gray, vestigial parent, we have homozygous dominant alleles for body color and homozygous recessive alleles for wing length, so the genotype is GGww.

Determine the \(F_{1}\) Generation Genotypes and Phenotypes

Since the parents are homozygous, all the offspring will have homozygous dominant alleles for body color and one dominant and one recessive allele for wing length, resulting in a genotype of GGWw. The phenotypes for all \(F_{1}\) offspring will be gray body color and long wings.

Determine the \(F_{2}\) Generation Genotypes by Crossing \(F_{1}\) Offspring

We will perform a monohybrid cross of two \(F_{1}\) individuals with genotypes GGWw. This will result in the following genotypes in the offspring: - 2/4: GGWW, GGWw (gray body, long wings) - 2/4: GGww (gray body, vestigial wings)

Determine the \(F_{2}\) Generation Phenotype Ratios

From the genotypes found in step 3, we can determine the phenotypic ratios of the \(F_{2}\) generation offspring: - 2/4: Gray body, long wings - 2/4: Gray body, vestigial wings