SAT Subject Biology Practice Question 392: Answer and Explanation
2. Consider this pedigree:
The allele causing the disorder (shaded individuals are affected) can best be described as
A. autosomal dominant
B. autosomal recessive
C. X-linked dominant
D. X-linked recessive
E. There is not enough information to determine.
Correct Answer: D
D First, the disorder skips generations (the parents of affected individuals do not display the disorder) so it is recessive, and choices A and C can be eliminated. Furthermore, all affected individuals are male, indicating that the disorder is sex-linked, and choice B can be eliminated. Finally, because the disease does not pass from father to son, it must be X-linked, and choice E can be eliminated.