Chapter 12, Problem 12STP

Summary Introduction

To determine:

The percentage of offspring that would be homozygous for the given traits.

Introduction:

A cross that involves hybrids for two traits is called a dihybrid cross. Punnett developed a method to predict the possible offspring of a cross between two known genotypes. It is easier to keep a track of the possible genotypes involved in a cross.

Answer to Problem 12STP

Percentage of offspring homozygous (dominant) for both traits is 1 out of 16= 6.25%.

Percentage of offspring homozygous (recessive) for both traits is 1 out of 16= 6.25%.

This can be checked by drawing a Punnett square for the dihybrid cross.

Explanation of Solution

An organism with genotype ( RrYy) will produce four types of gametes- male and female- each with either the R allele or r allele and either Y or y allele. If a dihybrid cross between two organisms with genotype ( RrYy) is performed, the possible combinations of possible alleles from each parent as shown by Punnett square are:

RRYY, RRYy, RrYy, rryy, RrYY, rrYY, Rryy, rrYy and RRyy .

This can be checked by drawing a Punnett square as shown below.

	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

Out of these the offspring with homozygous genotypes are RRYY (dominant) and rryy (recessive ).

Percentage of offspring homozygous (dominant) for both traits is 1 out of 16= 6.25%.

Percentage of offspring homozygous (recessive) for both traits is 1 out of 16= 6.25%.