Final answer:
In autosomal recessive inheritance, two affected parents cannot have an unaffected offspring as they both carry only the recessive alleles responsible for the genetic disorder.
Step-by-step explanation:
When considering patterns of inheritance for genetic disorders, it's important to understand what is expected in specific scenarios. With autosomal recessive inheritance, an affected offspring can only occur if both parents carry at least one recessive allele for the trait. Hence, for the given options:
- Option a) Two unaffected parents could be carriers (heterozygous) and still have an affected offspring, making this possible.
- Option b) Two affected parents cannot have an unaffected offspring because they can only pass on the recessive alleles responsible for the disorder, meaning all of their children will also be affected.
- Option c) One affected and one unaffected parent could have an unaffected offspring if the unaffected parent is either heterozygous or homozygous dominant, making this possible.
- Option d) Only option b is not possible for a recessive disorder.
The correct answer is b) Two affected parents have an unaffected offspring, as this would not be a possible outcome for a recessive disorder. This is because affected individuals have two copies of the recessive allele and would only be able to pass these alleles on to their offspring.