Question

Suppose a three-point testcross was conducted involving genes X, Y, and Z. If the most abundant classes of progeny are X Y z and x y Z and the rarest classes are x Y Z and X y z, which gene is in the middle?

Answer 1

QUESTION-1

ANSWER

Three-point cross-

Three-point cross uses three points of three genes to find out the order and distance between the genes.

Here in the given question, a three-point testcross was conducted involving genes X, Y, and Z.

The most abundant classes of progeny are  X Y z and x y Z.

The rarest classes of progeny are x Y Z and X y z.

To find out the middle gene,

First, you have to consider the most abundant progeny as the parental genotype and rarest ones as the recombinant genotype.

So here parental genotypes are- X Y z and x y Z.

and the recombinant genotype- x Y Z and X y z.

Next thing you have to do is to observe the allele which does not change its position with reference to the parental genotype.

If you look at first group i.e 1st parent and 1st recombinant,

Parent-  XYz

Recombinant-  xYZ.

Here Y allele doesn't change its position with reference to the other two alleles.

Then if you look at second group 2nd parent and 2nd recombinant,

Parent- xyZ

Recombinant- Xyz

Here also y allele doesn't change its position with reference to the other two alleles.

CONCLUSION- So the Yy gene is present in the middle.

GOOD LUCK.