Explain the inheritance pattern of Congenital Adrenal Hyperplasia (CAH), assuming it's an autosomal recessive condition.

Let 'A' represent the dominant allele for normal adrenaline production (no CAH).
Let 'a' represent the recessive allele for CAH.

Since CAH is a recessive condition, a person must have two recessive alleles ($aa$) to have the condition. Parents who do not have CAH but can have a child with CAH must both be heterozygous carriers. This means each parent has one dominant allele and one recessive allele.
Parent 1 genotype: $Aa$ (Normal, carrier)
Parent 2 genotype: $Aa$ (Normal, carrier)

Each parent will produce two types of gametes:
Parent 1 gametes: A, a
Parent 2 gametes: A, a

The Punnett square shows the possible combinations of alleles in their offspring.

From the Punnett square, the possible genotypes for the offspring are:

• $AA$: 25% chance (Normal, non-carrier)
• $Aa$: 50% chance (Normal, carrier)
• $aa$: 25% chance (Has CAH)

Explanation:
When both parents are heterozygous carriers ($Aa$), there is a 25% probability that their child will inherit the recessive allele ($a$) from each parent, resulting in the genotype $aa$. A child with the genotype $aa$ will express the recessive condition, CAH, even though neither parent has the condition themselves.

Here is the genetic diagram:
Parents' phenotypes: Normal (no CAH) $\times$ Normal (no CAH)
Parents' genotypes: $Aa \times Aa$
Parents' gametes: $A, a \quad \times \quad A, a$

Punnett Square:

Offspring genotypes: $1 AA : 2 Aa : 1 aa$
Offspring phenotypes: 3 Normal (no CAH) : 1 CAH

This diagram shows that there is a 1 in 4 chance for parents who are both carriers ($Aa$) to have a child with CAH ($aa$).