Question

Many of the color varieties of summer squash are determined by sev eral interacting loci: Wildtype squash are white, a recessive allele, a, causes yellow squash, while another recessive allele b, causes green squash.

a) How would you test if these alleles are mutations in the same gene? And what result would you expect if they are not in the same gene.

b) You do a cross to determine the relationship between genes A and genes B. You find B is epistatic to A. What cross did you perform? What was the result finding that led you to this conclusion?

Answer 1

Summer squash are weak stemmed tender annuals. Yhey have large cucumber like leaves, and seperates male and femafemale flowers appear on the same plant.

Common name - summer squash

Scientific name - Cucurbita pepo

Many of the color varieties are determined by several interlocating loci; AA or Aa gives white color, aaBB or aaBb gives yellow, and aaBb gives green.

An important task is to determine how many different grnes are represented by the mutations that determine the related pehenotypes, because this number defines the set of genes that affect the process under study. Hence it is necessary to have a test to find out if the mutations are alleles of one generation or different genes. This is referred by Complementation test.

Complementation is the product of wild type phenotype when two haploid genomes bearing different recessive mutations are united in the same cell.

However the demonstration of the recessive nature of the individual mutants is a crucial result that allows u to proceed with a complementation test. Dominant mutations cannot be used in the complementation test.

In a diploid organism, the complementation test is performed by intercrossing homozygous recessive mutants two at a time. The next step is to observe wether the progeny has the wild type phenotype.

This unites the two mutations as a haploid gamete to form a diploid nucleus in one cell i.e., the zygote. If recessive mutations represents alleles on the same genes then they will not complement because both genes represents loss gene functions​. These alleles could have different mutant sites, but they would be functionally identical i.e., both are non functional. However two recessive mutations in the different genes would have wild type function provided by the respective wild type alleles.

Epistasis

A condition in which one gene pair masks the impression of a non allelic grne pair is called epistasis.

In classical genetics, if genes A and B are mutated and each mutation by itself produces a unique phenotype but the two muations together show the same phenotype as the gene B mutation, then Gene B is epistatic and Gene A is hypostatic.

There is a very common example of baldness and brown hair. The gene for total baldness is epistatic to the gene of brown hair.