Genotype or phenotype??? color blind??? help help?

Question

what genotype or phenotype would parents have to have to have a child with this disease????

Answer 1

Color blindness is a s*x linked trait, so it differs from males to females.  For males, they would only need to have one affected X chromosome where for a female to be colorblind, she would need to have both X chromosomes affected.  If she would only have one affected X, she would have normal vision, but could pass on the allele for colorblindness to he children.    The way you can keep this straight is to use a superscript "c" (X^c) to show an affected X chromosome.  

So, for the genotype X^cY, the phenotype would be a colorblind male or for X^c X^c , the person would be colorblind female.

For the genotype X^c X, the person would be a female carrier.

XY would be a normal male, and XX would be a nornal female.

To pass this on to a male child, the allele would have to come from the mother (the father can only provide the "Y" for a male) - she could either be colorblind (X^cX^c, in which case all males will be colorblind) or a carrier (X^cX, in which case 1/2 of the male children will be colorblind).

To pass this on to a female child and have her be colorblind, the father would have to be colorblind, and the mother either be colorblind (in which case all the daughters would be colorblind as well) or the mother would have to be a carrier (in which case 1/2 of the daughters will be colorblind, and 1/2 carriers).

For a female child to be a carrier, she only needs to have one affected chromosome, so this could come from a colorblind father and a normal or carrier mother (in the case of a carrier, the daughter would inherit the unaffected chromosome), or a normal father and a colorblind or carrier mother (in this case the daughter would inherit the affected chromosome).