Spinal muscular atrophy autosomonal recessive disorder what are the chances a child would not have the recessive illegal if both parents are carriers

Spinal Muscular Atrophy (SMA) is indeed an autosomal recessive disorder, meaning a child needs to inherit two copies of the mutated gene—one from each parent—to have the condition.

If both parents are carriers of the SMA gene mutation, they each have one copy of the altered gene and one normal copy. The possible genetic combinations for their child are as follows:
- 25% (1 in 4) chance the child will inherit two normal genes (and thus be unaffected and not a carrier),
- 50% (1 in 2) chance the child will inherit one normal gene and one mutated gene (and thus be a carrier but not affected by the disorder),
- 25% (1 in 4) chance the child will inherit two mutated genes (and thus have SMA).

Therefore, the probability that a child would not inherit the recessive allele at all (i.e., receive two normal genes) when both parents are carriers is 25%.