Final answer:
The chance that the couple's first child would suffer from ALS is 50%, as the inheritance is autosomal dominant and Mary is heterozygous with a chance of passing on the allele for ALS to her child.
Step-by-step explanation:
The question refers to the chances of a child inheriting Amyotrophic Lateral Sclerosis (ALS), which is an autosomal dominant disorder. Since disorders like deafness and ALS are mentioned as dominant, not X-linked recessive, the figures you provided about X-linked recessive inheritance don't directly apply. We'll assume that 'P=0.5' means the probability of passing on the dominant allele from a heterozygous parent. Mary must be heterozygous for both traits, as she has both traits but has a husband who is normal (presumably homozygous recessive). If genes are 40 cM apart, the chance of recombination between them when passed to offspring is 40%. However, recombination here doesn't affect the chance of inheriting ALS specifically, but only if they inherit ALS and deafness together or separately.
Since the disorder is autosomal dominant, and assuming Mary is heterozygous for ALS, she has a 50% chance of passing this trait to her child, irrespective of the second trait for deafness. Her husband, being normal, can only pass the recessive allele. Therefore, each child has a 25% chance of being homozygous dominant (affected by ALS if it's a complete penetrance), 50% chance of being heterozygous (affected if penetrance is complete), and 25% chance of being homozygous recessive (unaffected).Thus, for the couple's first child to suffer from ALS, the probability, allowing for the dominant nature and the heterozygous state of Mary, will be 50%, which corresponds to the child inheriting the ALS allele from Mary. This probability does not consider the genetic distance since the question asks for the chance of the child having ALS, not both ALS and deafness.