Question

Waardenburg syndrome is an autosomal dominant disorder in which patients may exhibit a variety of clinical features, including patches of prematurely grey hair, white eyelashes, a broad nasal root, and moderate to severe hearing impairment. Occasionally, affected individuals display two eyes of different colors and a cleft lip and/or palate. Patients who possess a mutation in the PAX3 gene on chromosome 2 can present with all of these disparate signs and symptoms. Which of the following characteristics of genetic traits is illustrated by this example?

A. Anticipation
B. Imprinting
C. Incomplete penetrance
D. Locus heterogeneity
E. Pleiotropy

Answer 1

Waardenburg syndrome is characterized by various unrelated phenotypic traits resulting from a mutation in the PAX3 gene, illustrating the concept of pleiotropy, which occurs when one gene affects multiple traits.

Step-by-step explanation:

Waardenburg syndrome is an example of pleiotropy, where a single genetic mutation in the PAX3 gene influences multiple seemingly unrelated phenotypic traits. This autosomal dominant disorder is characterized by a variety of clinical features such as patches of prematurely grey hair, heterochromia (two different colored eyes), a broad nasal root, and hearing impairment, among others.

Autosomal dominant disorders like Waardenburg syndrome are caused by one defective allele and can be expressed even if only one parent passes on the affected gene. Other characteristics of genetic traits like incomplete penetrance or locus heterogeneity may also play a role in genetic disorders, but in this case, it is the multifaceted impact of a single gene's mutation that exemplifies pleiotropy. Pleiotropy contrasts with other genetic concepts such as anticipated genetic disorders where symptoms become worse with each generation (anticipation), or genetic imprinting where the expression depends on the parent of origin.