Chapter 5, Problem 23P

Summary Introduction

To analyze:

A cross between wild type soybean plants with pure breeding soybean plant having recessive phenotype gives the following gametes. The dominant traits are not showed in the table.

Phenotype	Number
Pale	$648$
Pale, oval	$64$
Pale, short	$10$
Pale, oval, short	$102$
Oval	$6$
Oval, short	$618$
Short	$84$
Wild type	$98$
Total	$1630$

By using the above information,

1. Predict alleles present on the homologous chromosome of the parental wild type soybean plant.

2. Determine the recombinant frequency between the adjacent genes on the chromosome.

3. Calculate the interference value for the given data.

Introduction:

The cross which involves the inheritance of three genes is called the trihybrid cross. According to the law of independent assortment, each allele separates from the other independently. Therefore, in trihybrid cross, there are different gametes produced, out of which two gametes are called parental gametes or non-recombinant and four are produced from single crossover and two produced from double crossover.

The parental gametes are produced during meiosis and do not undergo crossing over. Therefore, they match the parental genotype. Hence the different arrangement of dominant and recessive allele occurs at the chromosome. Parental gametes are present at the homologous chromosome.

Non-recombinant gametes account for high frequency than the recombinant gametes.

The recombination frequency depends upon the distance between the two genes. The recombination frequency suggests that if the distance between two genes is more, then crossing over in the genes occurs at a high rate. If the linked gene has a high recombination frequency, then they are more distant from one another.

The recombination frequency (r) of the syntenic gene is calculated by the formula-

$\text{r=}\frac{\text{Number of recombinant}}{\text{Total number of progeny}}$

Interference (I) value is used to predict the double crossover (expected but not produced). Interference is given as, I = 1- c …where c is the coefficient of coincidence.

If the I < 0, the condition is called negative interference, and if $\text{I = 0}$, the expected and observed interference is the same.