Table II. X chromosome instability in females (F) or males (M) of different genotypes.

Sex	Genotype	No. of cells	(nX)	(nX) + X	(nX) – X	(nX) + derX
Female	parp-1+/+parp-2–/–	30	29	0	1	0
Female	parp-1–/–parp-2+/+	21	21	0	0	0
Male	parp-1+/–parp-2–/–	35	35	0	0	0
Female	parp-1+/–parp-2–/–	132	66	19	33	14

(nX) = metaphases with normal number of X chromosomes: XX, for female, X for male; (nX) + X = metaphases with one X in surplus; (nX) – X = metaphases with one X missing; (nX) + derX = metaphases with any kind of X aneuploidy and a derivative of X chromosome.