https://www.khanacademy.org/science/health-and-medicine/executive-systems-of-the-brain/neurodevelopmental-disorders/a/what-is-down-syndrome 2021-04-29T08:03:34Z What is Down syndrome? article https://www.khanacademy.org/science/biology/classical-genetics/sex-linkage-non-nuclear-chromosomal-mutations/a/x-inactivation 2021-08-02T05:22:02.009586435Z X-inactivation How XX human females (and other female mammals) shut down one of their X chromosomes in each cell. Disorders of sex chromosome number: Klinefelter, triple X, and Turner syndromes. article https://www.khanacademy.org/science/ap-biology/heredity/chromosomal-inheritance-ap/a/aneuploidy-and-chromosomal-rearrangements 2025-11-24T21:00:40.80360556Z Aneuploidy & chromosomal rearrangements Aneuploidy and nondisjunction. Down syndrome and related disorders. Chromosomal rearrangements. article