Chapter 11, Problem 11STP

Summary Introduction

To find:

The percentage of offspring with homozygous genotype by using a Punnett square

Introduction:

A cross that involves hybrids for a single trait is called a monohybrid 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. An organism with two of the same alleles for a particular trait is called homozygous while an organism with two different alleles for a particular trait is called heterozygous.

Answer to Problem 11STP

Based on the followingPunnett square there are 50% offspring with homozygous genotype

	Y	y
y	Yy	yy
y	Yy	yy

Explanation of Solution

A heterozygous yellow- seed plant can be represented as Yy .

A green- seed plant can be represented as yy. (Since green is a recessive trait, it will be expressed only in homozygous condition.)

If a yellow- seed plant ( Yy ) is crossed with a green- seed plant ( yy ), there are only two possible genotypes; Yy and yy .

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

	Y	y
y	Yy	yy
y	Yy	yy

So, the number of plants with homozygous genotype is 2 and heterozygous genotype is also 2. Hence the percentage of offspring with homozygous genotype is 50%.