Chapter 11, Problem 10STP

Summary Introduction

To show:

The results of a cross between a heterozygous yellow- seed plant and a green- seed plant 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 10STP

Crossbetween a heterozygous yellow- seed plant and a green- seed plant can be shown by using a Punnett square as follows:

	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.)

AYyyellow - seed plant will produce two types of gametes- male and female- each with either the Y allele or y allele. Ayy green seed plant will produce two types of gametes- male and female- both with y allele. If a yellow- seed plant ( Yy ) is crossed with a green- seed plant ( yy ), there are only two possible genotypes; Yy and yy . So the resulting phenotypic ratio will be 1: 1 yellow to green as equal number of yellow and green- seed plants will be produced.

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

	Y	y
y	Yy	yy
y	Yy	yy