Question

common chromosomal abnormalities and their frequencies
name of abnormality | chromosomal abnormality | frequency
trisomy 21 (down syndrome) | extra copy of chromosome 21 | 1/800
trisomy 18 (edwards syndrome) | extra copy of chromosome 18 | 1/5000
trisomy 13 (patau syndrome) | extra copy of chromosome 13 | 1/16000
monosomy x (turner syndrome) | only one sex chromosome; only the x chromosome | 1/2500
klinefelter’s syndrome | extra x sex chromosome | 1/750
the table above shows five different types of chromosomal abnormalities that can occur during meiosis. they result in either an individual having too many or too few chromosomes in their genome. what is the most likely cause of these chromosomal abnormalities?
a deletion of chromosomes
b insertion of chromosomes
c translocation of chromosomes
d nondisjunction of chromosomes

Explanation:

The table lists abnormalities with extra or missing chromosomes (e.g., Trisomy 21 has an extra chromosome 21, Turner Syndrome has one X). These numerical chromosome errors during meiosis are caused by nondisjunction—failure of chromosomes to separate properly. Deletion, insertion, and translocation affect chromosome structure, not number.

Answer:

D. nondisjunction of chromosomes