Color blindness is a recessive trait. the gene for color blindness is on the x- chromosome. the family tree below shows the trait of color blindness. the only unknown is the mother in the first generation. to what must be true about the mother? o a. she has at least one recessive color blindness allele. o b. she only has one x chromosome. o c. she is color-blind, o d. she has two recessive color blindness alleles.