Question

Females with the genotype X^CBX^cb (heterozygous for the red-green colorblindness allele) are rarely colorblind although some have only partial color vision. Speculate on why this is true.

Answer 1

The red-green color blindness is X-linked recessive traits. It is known that male has one X chromosome and one Y chromosome. So, if he inherits recessive allele from his mother, he will be colorblind.
It is more complicated for females because they have two X chromosomes. Similarly to Mendelian monohybrid cross, a female which is recessive homozygous will be colorblind (X^cbX^cb). But a heterozygous female (X^CBX^cb) will be rarely color because she has one dominant allele.