The origin of Turner syndrome is a monosomy in X chromosomes of the individual. The genotype of the person would be XO. This occurs due to a meiotic nondisjunction.
The origin of Down syndrome is a trisomy in chromosome 21. The person has three copies of the chromosome 21 instead of only 2. This is due to meiotic nondisjunction or a Robertsonian translocation.
The origin of Klinefelter syndrome is an extra X chromosome. The genotype of the male would be XXY. Such people have impaired IQ and are sterile.
| Klinefelter syndrome | Down syndrome | Turner syndrome |
| It occurs in males. | It occurs in both sexes. | It occurs in females. |
| It is observed to have XXY condition in males. | It is observed with trisomy 21. | It is observed with XO condition is females. |
| It occurs when one extra X chromosome is added to normal XY genotype of males. | It occurs due to meiotic nondisjunction or due to Robertsonian translocation. | It occurs due to meiotic nondisjunction. |