Sandra excels in reading and spelling but struggles with mathematics. She is shorter than her peers and has a webbed neck. Her doctor has determined that she has one X chromosome missing. Sandra most likely has:

The correct answer is - turner syndrome.

Explanation:

Turner syndrome is is a chromosomal condition are due to the missing or partially missing one sex chromosome in females. It is specific to females only. It leads to different types of problems such as short stature, ovarian hypofunction, infertility, delayed puberty, webbed neck, learning disabilities, and many other symptoms.

As Sandra has short stature, the problem in the learning and doctor also determined that she has one X chromosome missing so it can be determined by that she has turner syndrome.

Thus, the correct answer is - turner syndrome.