The homozygous condition HbsHbsresults in sickle cell anaemia whereas HbAHbs has the sickling trait. What is the probability that a couple with the sickling trait will give birth to one normal child?
The probability of a child inheriting the normal hemoglobin allele from two parents with sickle cell trait.
Given:
- Both parents have sickle cell trait (Hb A HbS)
- Sickle cell trait is a heterozygous condition, meaning the person has one normal allele(HbA), and one sickle cell allele(HbS).
Note that each parent can contribute either the Hb A or HbS allele and the child's genotype will be a combination of the alleles from each parent.
Using a Punnett square to determine the possible genotypes of the offspring as shown in the diagram above, the Punnett square will have the possible alleles of the first parent across the top and the possible alleles of the second parent along the side.
Identifying the genotype for a normal child, a normal child will have two copies of the normal allele, resulting in the genotype 
HbAA.
From the Punnett square, the probability of HbAA is \(\frac{1}{4}\)
The probability of a normal child HbAA is \(\frac{1}{4}\).
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