Final answer:
Autosomal dominant disorders, which include Huntington's disease, Marfan syndrome, and achondroplastic dwarfism, require only one copy of the mutated gene to manifest symptoms. The inheritance pattern is vertical, affecting both males and females equally. Color blindness being autosomal dominant is incorrect; it is typically an X-linked recessive condition.
Step-by-step explanation:
Inheritance of Autosomal Dominant Disorders
The student's question relates to the inheritance pattern of an autosomal dominant disorder observed in an 18-month-old patient. If an individual has an autosomal dominant disorder like Huntington's disease, achondroplastic dwarfism, or Marfan syndrome, it means they possess at least one mutated allele causing the disorder. Such diseases are characterized by their ability to manifest with just one copy of the defective gene, unlike autosomal recessive disorders such as cystic fibrosis (CF), which require two copies, one from each parent, for the disease to present. In the context of the provided pedigree, determining whether ALD is neonatal or X-linked involves analyzing the pattern of inheritance and the affected family members' genders. Typically, in autosomal dominant disorders, there is a vertical transmission of the disease, meaning the defective gene is passed down through generations, affecting both males and females equally.
Given the information that males can be carriers of red-green color blindness because it is autosomal dominant is factually incorrect; red-green color blindness is in fact usually an X-linked recessive condition. Therefore, it is important to accurately diagnose genetic conditions and understand their inheritance patterns for proper counselling and prediction of recurrence in offspring.