A color-blind, chromatin-positive male child (one Barr body) has a maternal grandfather who was color-blind. The boy's mother and father are phenotypically normal. Construct and support a rationale whereby the chromosomal and genetic attributes of the chromatin-positive male are fully explained.

The male child is having Kleinfelter's syndrome.

Explanation:

In the Klinefelter's syndrome, the number of chromosomes is 47 ie 2X Y

It is given that he is chromatin-positive male i.e colour blind.  It can be assumed that he received two X chromosome from his mother in which one turned in to barr body. Colour blindness is an X-linked recessive trait.

Both the X chromosomes have an allele for colour blindness and nondisjunction has taken place in mother's gametes, making 2X chromosome.

It can be concluded that the chromosome having colour bling gene got expressed whereas the other chromosome became barr body.