Chapter 11.2, Problem 5MI

Summary Introduction

To determine:

The reason that a normal couple can give birth to a child having sickle cell anemia.

Introduction:

During the process of sexual reproduction, the parents produce haploid gametes. These haploid gamete contain 1 set of chromosomes for each trait. During fertilization event, two gametes fuse together and produce a diploid zygote, which eventually becomes the mature organism.

Explanation of Solution

The carrier is the individual, which is not infected with the disease, but they have an allele responsible for the disease. They are heterozygotes and have both dominant and recessive allele. The dominant allele masks the effect of recessive allele, which make them disease free.

Sickle cell anemia is a condition, which is caused by recessive allele. In case, there is a mating between two individuals that are carrier there are 25% chances of inheritance of homozygous recessive condition (refer to the Punnett square below). So, the carrier individuals may pass defective alleles to the child, which could cause sickle cell anemia.

Considering A as normal and a as defective allele below is the result of mating of two carriers ( Aa*Aa )

	A	A
A	AA normal	Aa normal
a	Aa normal	aa affected