Expert: Florence M Rollwagen - 11/30/2008

Question
color blindness is a sex-linked recessive trait. Alice has normal color vision, and
her husband is not color blind, but their son is colorblind. What is the phenotype
and genotype of Alice, her husband and her son?
Show using a punnett square the above result:
Key xC= color blind trait

Answer
Hi again, Carlos:  I can't answer questions privately.  If you have more questions, please submit them through AllExperts.

Thanks,
FMR

Hi Carlos:  Thanks for your question.

Red-green color blindness is a sex linked trait.  That means it is carried on the X chromosome.  Females have 2 X chromosomes, males one.  So females can be the carrier of a trait while being phenotypically normal.  Males, since they have only one X chromosome, cannot carry this allele.  If they inherit the X chromosome with the trait they will exhibit color blindness.

So the woman is X(C)X(c), and the man is X(C)Y.  The upper case (C) means normal color vision, the lower case (c) means color blindness.  The female can donate only one X chromosome to her son, so if the X(C) chromosome is inherited, the son will have normal vision, if the X(c) chromosome is inherited, the son will be color blind.

This format will not allow me to show the Punnett square, but go to this link for more   information:http://library.thinkquest.org/C004367/be1.shtml

Scroll down to sex-linked traits for the punnett square.

Hope this helps!  Write back if you have more questions.

FM Rollwagen, PhD