If two people who are both carriers (heterozygotes) for a genetically inherited fatal recessive disease decide to become parents, what will be the odds that their children will also be carriers?

If two people are carriers (heterozygotes) of a genetically inherited fatal recessive disease, that means each of them has one copy of the normal allele (n) and one copy of the disease-causing allele (d). When they decide to have a child, each parent can pass on either their normal allele or their disease allele to their offspring.

To work out the odds of their children being carriers, we can use a Punnett square, which is a grid that shows the possible genotypes of the offspring given the genotypes of their parents.

The parental genotypes will be:

Parent 1: N(d) - One normal allele (N) and one disease allele (d) Parent 2: N(d) - Same as parent 1

Here is how we construct the Punnett square:

``` N d ---------------- N | NN Nd | ---------------- d | Nd dd | ---------------- ```

Each box within the Punnett square represents a possible genotype for the offspring:

- NN: The child does not carry the disease allele (25% chance). - Nd: The child is a carrier like the parents. There are two of these boxes (50% chance in total, 25% for each box). - dd: The child has two disease alleles, and thus will inherit the disease (25% chance).

Based on the Punnett square, there is a 50% chance that the children will be carriers of the disease, just like their parents.

Extra: Genetics is the study of heredity and the variation of inherited characteristics. In this case, we're talking about an autosomal recessive disorder, which means that two copies of an abnormal gene must be present for the disorder to develop.

In terms of inheritance:

- Recessive: The trait is expressed only when two copies of the recessive allele are present (hence "recessive"). If there is one dominant and one recessive allele, the dominant trait is usually expressed. - Heterozygous: Having two different alleles at a genetic locus (e.g., one normal and one disease allele, which in our case are designated N and d).

Autosomal recessive inheritance often involves important considerations for genetic counseling. Couples who are aware that they are carriers for a recessive disorder may seek counseling for understanding their risks in having affected children, for planning their families, and exploring options like genetic testing.