My son have colour visiondeficiency although there is no history of inheritance from either side. his eye checkup is normal. pl suggest?

Maternal inheritanc : If you son has classic color deficiency, it is on his x chromosome which he got from his mother. She herself would probably be color normal and her abnormal x would have gotten to her from either parent - her mother (your son's grandmother) if that is the source, would also be color normal. He will have normal sons but daughters who will all be carriers without color deficit themselves.

Retest: Most color vision deficits are inherited through the mother. On the x chromosome. Females of the family are carriers of the gene but only males are affected. Rarely a child can have a new genetic defect. The diagnosis is made by a trained pediatric ophthalmologist or retina specialist. Reading vision can be normal.