Which of the following human diseases is inherited as a simple recessive trait?

• A. Hemophilia
• B. Cystic fibrosis
• C. Huntington's disease
• D. Marfan syndrome

Answer: (B)

Verified step by step guidance

1. Understand the concept of a recessive trait: A recessive trait is one that is expressed in an individual only when two copies of the recessive allele are present. This means the individual must inherit one recessive allele from each parent.
2. Identify the inheritance pattern of each disease: Research the genetic basis of each disease listed to determine if it is inherited as a recessive trait.
3. Hemophilia is typically inherited as an X-linked recessive trait, meaning it is associated with the X chromosome and more commonly affects males.
4. Cystic fibrosis is inherited as an autosomal recessive trait, meaning it requires two copies of the recessive allele on a non-sex chromosome for the disease to be expressed.
5. Huntington's disease and Marfan syndrome are inherited as autosomal dominant traits, meaning only one copy of the dominant allele is needed for the disease to be expressed. Therefore, cystic fibrosis is the disease inherited as a simple recessive trait.