The following progeny are obtained from a test cross of a trihybrid wild-type plant to a plant with the recessive phenotypes compound leaves (c), intercalary leaflets (i), and green fruits (g). (Traits not listed are wild type.) The test-cross progeny are as follows:

Phenotype                                                                           Number
Compound leaves                                                                  324
Compound leaves, intercalary leaflets                                     32
Compound leaves, green fruits                                                  5
Compound leaves, intercalary leaflets, green fruits                 51
Intercalary leaflets                                                                     3
Intercalary leaflets, green fruits                                              309
Green fruits                                                                              42
Wild type                                                                                  49
                                                                                               815

Calculate the frequencies of recombination between the adjacent genes in the map.

Verified step by step guidance

1. Identify the parental and recombinant phenotypes by looking at the numbers of progeny. The most frequent phenotypes are the parental types, while the least frequent are the double recombinants.
2. Determine the gene order by comparing the double recombinant phenotypes with the parental phenotypes. The gene that differs in the double recombinants is the middle gene.
3. Calculate the recombination frequency between the first and middle gene by adding the number of single recombinants for these genes and the double recombinants, then divide by the total number of progeny.
4. Calculate the recombination frequency between the middle and last gene by adding the number of single recombinants for these genes and the double recombinants, then divide by the total number of progeny.
5. Express the recombination frequencies as percentages to represent the genetic map distances between the genes.

Key Concepts

Test Cross

A test cross is a genetic cross between an individual with an unknown genotype and a homozygous recessive individual. This method helps determine the genotype of the unknown parent by analyzing the phenotypes of the offspring. In this scenario, the wild-type plant is crossed with a plant exhibiting recessive traits, allowing for the observation of phenotypic ratios in the progeny to infer genetic linkage and recombination frequencies.

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, often expressed as a percentage. This frequency provides insight into the physical distance between genes on a chromosome, with higher frequencies indicating greater distances and lower frequencies suggesting closer proximity.

Genetic Linkage

Genetic linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. Linked genes do not assort independently, which can affect the expected ratios of phenotypes in offspring. Understanding genetic linkage is crucial for interpreting the results of a test cross, as it influences the recombination frequencies and the distribution of traits among progeny.