Question

A 20-year-old female presents for an infertility

workup. She has never had a menstrual period.
She is short with a broad chest, webbed neck,
and low-set ears. It is demonstrated that she has
an abnormal karyotype.
The cause of the woman's abnormal
karyotype
is which one of the following?
(A) Maternal nondisjunction
(B) Paternal nondisjunction
(C) Both maternal and paternal
nondisjunction
(D) Either maternal or paternal
nondisjunction
(E) A reciprocal translocation
(F) A Robertsonian translocation

Answer 1

The 20-year-old female's phenotype is indicative of Turner syndrome, caused by the presence of only one X chromosome. The most likely cause of this abnormal karyotype is paternal nondisjunction.

Step-by-step explanation:

The case described presents a 20-year-old female with characteristics such as never having a menstrual period, short stature, a broad chest, webbed neck, and low-set ears.

These features are indicative of Turner syndrome, which is characterized by the presence of only one X chromosome in a female (45,X) instead of the usual two.

This chromosomal abnormality is typically caused by nondisjunction during the formation of the egg (maternal nondisjunction) or sperm (paternal nondisjunction). However, since Turner syndrome is almost exclusively associated with the loss of paternal sex chromosome, the most likely cause of this abnormal karyotype is paternal nondisjunction (Option B).