Final answer:
Autosomal recessive inheritance involves two carrier parents each contributing a recessive allele leading to a 25% chance of their offspring having a recessive disorder. There is also a 50% chance their child will be a carrier and a 25% chance of being unaffected. Some recessive disorders like Tay-Sachs can be lethal if the child inherits two recessive alleles.
Step-by-step explanation:
Autosomal recessive inheritance occurs when both parents are carriers of a recessive allele and each contributes this allele to the embryo. In this scenario, each child has a 25% chance of being affected by a recessive disorder, such as cystic fibrosis, if the disease-causing allele is inherited from both parents. Carrier parents, denoted as heterozygous (Ff), are not affected themselves because they possess one normal allele (F) that is dominant over the recessive disease allele (f).
During gamete formation, alleles segregate, ensuring that each gamete carries only one allele for each gene. When two carriers mate, there's a 50% probability that their child will also be a carrier (Ff). However, there's also a 25% chance that the child will inherit two normal alleles (FF) and be unaffected, and likewise, a 25% chance of inheriting two recessive alleles (ff) and expressing the disorder.
In certain extreme cases, such as with Tay-Sachs disease, these recessive genetic disorders can be lethal. Tay-Sachs is characterized by a faulty allele which, if inherited from both parents, leads to early childhood death. In these instances, a recessive allele maintains its presence in a population even though it leads to fatal consequences when present in a homozygous recessive individual (ff).