Genetic diseases caused by chromosomal abnormalities

down syndrome

3 copies of chromosome 21. Trisomy 21.
In 90% of cases, the extra chromosome comes from the mother.

Turner Syndrome

Have only one X chromosome.

This is an example of monosomy. Only 1 parent contributes an X
chromosome. In 75-80% of cases, the X chromosome comes from the mother

Klinefelter Syndrome

have one Y and two X chromosomes.
(trisomy). The extra X chromosome can come from either parent.

what creates the conditions for this?

non-disjunction – pair of
chromosomes fails to separate during formation of gametes