Which condition is characterized by 45 chromosomes with a single X chromosome and affects female fetuses?

• A. Turner syndrome
• B. Down syndrome
• C. Klinefelter syndrome
• D. Triple X syndrome

Answer: (A)

Turner syndrome is the condition described here. It arises from monosomy X, meaning there is only one sex chromosome present (45 total chromosomes) and no Y chromosome, so the individual develops as female. The missing second sex chromosome leads to ovarian failure and distinctive features such as short stature, a webbed neck, lymphedema at birth, and widely spaced nipples, with possible congenital heart defects. Because there is no second X to drive typical female pubertal development, affected individuals often have primary amenorrhea and infertility, though growth hormone and estrogen therapies can help manage some aspects.

Other chromosomal patterns explain why the other options don’t fit: Down syndrome involves an extra chromosome 21 (47 total), Klinefelter syndrome is a male with an extra X chromosome (47,XXY), and Triple X syndrome is a female with an extra X chromosome (47,XXX). The key here is the 45-chromosome count with a single X in a female.