A wild-type trihybrid soybean plant is crossed to a pure-breeding soybean plant with the recessive phenotypes pale leaf (l), oval seed (r), and short height (t). The results of the three-point test cross are shown below. Traits not listed are wild type.

Calculate the recombination frequencies between the adjacent genes.

Verified step by step guidance

1. Step 1: Identify the parental phenotypes and the double crossover phenotypes. The parental phenotypes are the most frequent phenotypes in the data, while the double crossover phenotypes are the least frequent. In this case, the parental phenotypes are 'Pale' (648) and 'Oval, short' (618), and the double crossover phenotypes are 'Oval' (6) and 'Pale, short' (10).
2. Step 2: Determine the gene order by comparing the parental phenotypes with the double crossover phenotypes. The gene that differs between the parental and double crossover phenotypes is the middle gene. For example, compare the traits in 'Pale' and 'Oval' or 'Oval, short' and 'Pale, short' to identify the middle gene.
3. Step 3: Group the phenotypes into single crossover classes for each gene pair. For example, group the phenotypes that differ by one gene from the parental phenotypes. These groups will help calculate the recombination frequencies between adjacent genes.
4. Step 4: Calculate the recombination frequency for each gene pair. Use the formula: $\frac{\mathrm{Number}\mathrm{of}\mathrm{recombinants}}{\mathrm{Total}\mathrm{number}\mathrm{of}\mathrm{offspring}}$. Add the number of single crossover and double crossover offspring for each gene pair, then divide by the total number of offspring (1630).
5. Step 5: Convert the recombination frequencies into map distances (in centimorgans, cM). Each 1% recombination frequency corresponds to 1 cM. This will give you the genetic distances between the adjacent genes.

Key Concepts

Recombination Frequency

Recombination frequency is a measure of the likelihood that two genes will be separated during meiosis due to crossing over. It is calculated by dividing the number of recombinant offspring by the total number of offspring, then multiplying by 100 to express it as a percentage. This frequency helps in determining the genetic distance between genes on a chromosome.

Trihybrid Cross

A trihybrid cross involves organisms that are heterozygous for three different traits. In this case, the wild-type soybean plant carries dominant alleles for traits such as leaf color, seed shape, and height, while the pure-breeding plant has recessive alleles. Analyzing the offspring from this cross allows researchers to study the inheritance patterns and interactions of multiple genes.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this scenario, the observed phenotypes and their counts provide insight into the inheritance of traits. By analyzing these ratios, one can infer the genetic linkage and recombination events that occurred during gamete formation.