Question

The idea is about genetic testing not about getting a specific answer.

In a genetics experiment of a pathway, loss of function in gene X or gene Y causes a blue phenotype, and loss of function in gene Z causes a green phenotype.

What experiments could you use to find the order and regulatory relationships of all the genes? Assume you have all the types of alleles you would want and explain what you would observe in your experiment if gene X --| gene Z --| gene Y.

You then find a loss of function mutant called mutant M that expresses a green phenotype. How would you figure out using only a classic genetic test if mutant M is a new allele of gene Z or if it is an allele of a new gene?

Answer 1

a)

Experiments :

To find out the order and regulatory relationships of all the genes, I would take true breeding plants and cross them as follows :

Let alleles of gene X, Y and Z be (X,x) , (Y,y) and (Z,z) where capital letter signifies a dominant allele and small letter signifies a recessive allele.

First Cross - xxZZ x XXzz

Second Cross - yyZZ x YYzz

Third cross - xxYY x XXyy

After performing these crosses , we can observe the colour of F1 and F2 offsprings and find out about the order of genes and their regulatory relationships.

b)

If X ---I Z -----I Y, then the following results will be observed,

First Cross F1 generation - It will have a green phenotype

Second Cross F1 generation - It will have have a blue phenotype

Third cross F1 generation - It will have blue phenotype.

c) I would perform a test- cross of the individual with mutant allele M with a double recessive individual (recessive for any 2 of the three genes) to find out if mutant M allele is a new allele of gene Z or it is an allele of a new gene.