Chapter 10, Problem 32A

Summary Introduction

To write:

A plan indicating the way by which a flock of pure-breeding white sheep could be developed.

Introduction:

Each organism receives two version of the same gene, and these versions are termed as alleles. If different alleles are present in the gene, then the dominant allele will express itself and mask the effect of recessive allele. So, there are two types of alleles, dominant allele and recessive allele.

Explanation of Solution

Recessive allele can only be expressed in homozygous form (aa), but a dominant allele can be expressed in both homozygous (AA) and heterozygous (Aa) forms.

Here, white wool sheep is dominant over black wool sheep. Now in a flock, some sheep are heterozygous; this means these sheep will be white in color. So, establishing pure breeding lines will be a time consuming process as after some generations only pure breeding line can be obtained. For this, two white color sheep should be mated, if any of their child is black, then it means that white sheep are heterozygotes. Now, only white wool sheep should be mated for at least 3 generations. As after these generations, some homozygotes for white wool will be present, and they can carry on the pure breeding line.