Chapter 15, Problem 7STP

Summary Introduction

Introduction:

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. The male gametes are written across the horizontal side and female gametes are written on the vertical side of the Punnett square. The possible combinations of each male and female gamete are written on the inside of each corresponding square.

Answer to Problem 7STP

Correct answer :

The correct answer is option D. 100%

Explanation of Solution

Explanation/justification for the correct answer:

Option D. 100%- A homozygous animal for the dominant gene can be represented as BB.

A homozygous animal for the recessive gene can be represented as bb.

The children will have only one possible genotypes; Bb.

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

	B	B
b	Bb	Bb
b	Bb	Bb

Based on the Punnett square, there are 100% offspring who have the dominant gene ‘ B’ . The genotypes of the children will be 100% heterozygous for the dominant gene.

So, all the children will have dominant gene. Hence this is the correct option.

Explanation for incorrect answer:

Option A. 25%- Based on the Punnett square, there are 100% offspring who have the dominant gene ‘ B’ . The genotypes of the children will be 100% heterozygous for the dominant gene.

So, all the children will have dominant gene. Hence this is not the correct option.

Option B. 50%- Based on the Punnett square, there are 100% offspring who have the dominant gene ‘ B’ . The genotypes of the children will be 100% heterozygous for the dominant gene.

So, all the children will have dominant gene. Hence this is not the correct option.

Option C. 75%- Based on the Punnett square, there are 100% offspring who have the dominant gene ‘ B’ . The genotypes of the children will be 100% heterozygous for the dominant gene.

So, all the children will have dominant gene. Hence this is not the correct option.