X-inactivation example: Calico cat
- The orange patch is made up of cells in which the X with the orange allele () is active, while the X with the black allele () is compacted into a Barr body.
- The black patch is made up of cells in which the X with the black allele () is active, while the X with the orange allele () is compacted into a Barr body.
Sex chromosome aneuploidies
- Triple X syndrome, in which a woman has an XXX genotype, which occurs in about out of every female newborns. Women with an XXX genotype have female sex characteristics and are fertile (able to have children). In some cases, triple X syndrome may be associated with learning difficulties, late development of motor skills in infants, and problems with muscle tone.
- Klinefelter syndrome, in which males have an extra X chromosome, leading to a genotype of XXY. (In rarer cases, Klinefelter syndrome can involve several extra Xs, leading to an XXXY or XXXXY genotype.) Affected men may be infertile or develop less dense body and facial hair than other men. Klinefelter syndrome is thought to affect out of every to male newborns.