Table : TABLE 2.1 The 23rd Pair and X-Linked Color Blindness

23rd Pair	Phenotype	Genotype	Next Generation
1. XX	Normal woman	Not a carrier	No color blindness from mother
2. XY	Normal man	Normal X from mother	No color blindness from father
3. XX	Normal woman	Carrier from father	Half her children will inherit her X. The girls with that X will be carriers; the boys with her X will be color-blind.
4. XX	Normal woman	Carrier from mother	Half her children will inherit her X. The girls with her X will be carriers; the boys with her X will be color-blind.
5. XY	Color-blind man	Inherited from mother	All his daughters will have his X. None of his sons will have his X. All his children will have normal vision, unless their mother also had an X for color blindness.
6. XX	Color-blind woman (rare)	Inherited from both parents	Every child will have one X from her. Therefore, every son will be color-blind. Daughters will be only carriers, unless they also inherit an X from the father, as their mother did.

Note: On this chart, the red X means that it contains the gene for color blindness.