A fruit fly with a gray body and red eyes (genotype BbPp) is mated with a fly having a black body and purple eyes (genotype bbpp).
What ratio of offspring would you expect if the body-color and eye-color genes are on different chromosomes (unlinked)?
When this mating is actually carried out, most of the offspring look like the parents, but 3% have a gray body and purple eyes, and 3% have a black body and red eyes.
Are these genes linked or unlinked?
What is the recombination frequency?

Verified step by step guidance

1. Step 1: Begin by analyzing the genotypes of the parent fruit flies. The first parent has the genotype BbPp, which means it is heterozygous for both body color (B = gray, b = black) and eye color (P = red, p = purple). The second parent has the genotype bbpp, which is homozygous recessive for both traits.
2. Step 2: Since the problem states that the body-color and eye-color genes are on different chromosomes (unlinked), use a Punnett square to determine the expected offspring ratios. For unlinked genes, the alleles segregate independently during gamete formation. Calculate the possible gametes for each parent: BbPp produces BP, Bp, bP, and bp, while bbpp produces only bp.
3. Step 3: Combine the gametes from both parents in a Punnett square to determine the genotypes and phenotypes of the offspring. The expected phenotypic ratio for unlinked genes is 1:1:1:1, corresponding to gray body/red eyes, gray body/purple eyes, black body/red eyes, and black body/purple eyes.
4. Step 4: Examine the actual offspring data provided in the problem. Most offspring resemble the parents, but 3% have gray body/purple eyes and 3% have black body/red eyes. This deviation from the expected 1:1:1:1 ratio suggests that the genes may be linked, meaning they are located close together on the same chromosome and do not assort independently.
5. Step 5: Calculate the recombination frequency to determine the degree of linkage. Recombination frequency is calculated as the percentage of recombinant offspring (those with new combinations of traits, such as gray body/purple eyes and black body/red eyes) out of the total offspring. Use the formula: \( \text{Recombination Frequency} = \frac{\text{Number of Recombinant Offspring}}{\text{Total Number of Offspring}} \times 100 \). Substitute the given values to find the recombination frequency.

Key Concepts

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, genotype versus phenotype, and the segregation and independent assortment of genes during gamete formation. This framework is essential for predicting the ratios of offspring phenotypes in genetic crosses.

Linkage and Recombination

Linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together, while recombination occurs during meiosis when homologous chromosomes exchange genetic material. The degree of linkage can be quantified by the recombination frequency, which indicates the proportion of offspring that exhibit recombinant phenotypes. A lower recombination frequency suggests that genes are linked, while a higher frequency indicates they are unlinked.

Punnett Squares and Phenotypic Ratios

Punnett squares are a tool used to predict the genotypic and phenotypic ratios of offspring from a genetic cross. By organizing the possible gametes from each parent, one can visualize the expected ratios of different traits in the offspring. In this scenario, calculating the expected ratios based on the unlinked genes helps determine the likelihood of observing specific phenotypes, which can then be compared to actual results to assess gene linkage.