Tutorial: Inheritance of an X-linked recessive trait

Red-green color blindness is X-linked in humans. If a male is red-green color blind, and both parents have normal color vision, which of the male's grandparents is most likely to be red-green color blind? Parents
If both parents have normal vision, the mother of the affected male must be heterozygous for the X-linked, recessive alleles for red-green color blindness. The father of the affected male could not have been the source of the red-green color blind allele since fathers can only pass X-linked traits to their daughters, and Y chromosomes to their sons. Grandparents
The two possible pedigrees for inheritance from a maternal grandparent are shown in the pedigree charts labeled A andWhich of the mother's parents, the maternal grandmother (pedigree chart B) or maternal grandfather (pedigree chart A), is more likely to both be
1. red-green color blind, 2. the source of the allele inherited by their grandson? Males with only a single X chromosome are more commonly affected by X-linked, recessive traits than are females with two X chromosomes. Why?
A male need only inherit the recessive allele from a heterozygous female carrier. A female would need to inherit the recessive allele from both parents, an affected father and a carrier (or affected) mother. B.