Counselor Preparation Comprehensive Practice Examination

The correct response identifies Hemophilia as not being classified as an autosomal disease. This distinction is based on the genetic inheritance pattern of Hemophilia, which is primarily linked to the X chromosome, making it an X-linked recessive disorder. In X-linked disorders, the gene responsible for the condition is located on the X chromosome, and since males have one X and one Y chromosome, they are often more severely affected by X-linked conditions than females, who have two X chromosomes and may be carriers without showing symptoms.

In contrast, the other conditions listed—Phenylketonuria, Sickle Cell Anemia, and Tay-Sachs Disease—are all autosomal recessive disorders that occur because of mutations on non-sex chromosomes (autosomes). Individuals must inherit two copies of the mutated gene (one from each parent) to express the disease. This autosomal inheritance is characterized by the probabilities of inheritance being the same for both sexes.

Understanding the differences in inheritance patterns helps in recognizing how these diseases are passed through generations, illustrating the significance of genetic counseling and testing in managing and understanding these conditions.