Counselor Preparation Comprehensive Practice Examination

Which syndrome is characterized by having a single X chromosome?

1. Klinefelter's Syndrome

2. Turner Syndrome

3. Down Syndrome

4. Fragile X Syndrome

The correct answer is: Turner Syndrome

Turner Syndrome is characterized by the presence of a single X chromosome in females, resulting in a total of 45 chromosomes instead of the typical 46. This condition arises from a chromosomal anomaly where one of the X chromosomes is completely or partially missing. Turner Syndrome can lead to a variety of physical and developmental features, such as short stature, primary amenorrhea, and specific physical traits like a webbed neck and broad chest. In contrast, Klinefelter's Syndrome involves an extra X chromosome in males, leading to a total of 47 chromosomes (XXY). Down Syndrome is caused by an extra copy of chromosome 21, resulting in a total of 47 chromosomes as well. Fragile X Syndrome is a genetic condition resulting from a mutation on the FMR1 gene located on the X chromosome, but it does not involve the overall number of X chromosomes being reduced. Therefore, Turner Syndrome stands out distinctly for being defined by a single X chromosome.