A woman with a normal vision whose father was colour blind marries a man with normal vision whose father was also colour blind. This couple has a colour blind daughter with normal complement of chromosomes. Is infidelity suspected?

Yes, man's father can only pass down y chromosome to him, which does not carry colorblind gene. Need two recessive colorblind genes on the X chromosomes to have colorblind daughter.

The occurrence of color blindness in a daughter of parents who have normal vision is quite rare, but it is possible due to the inheritance patterns of genes related to color vision. In this case, there is no need to suspect infidelity. Allow me to explain the genetics behind this situation.

Color blindness is a sex-linked trait, meaning it is carried on the sex chromosomes, specifically the X chromosome. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The gene associated with color blindness is located on the X chromosome.

In your scenario, let's label the mother as XcX and the father as XY. The "Xc" represents the color blindness gene, while the "X" represents the normal version of the gene. Since the father is color blind, he has one X chromosome with the color blindness gene (Xc), and the mother has one normal X chromosome (X).

When it comes to their daughter's inheritance, there are two possible outcomes:

1. The daughter inherits the normal X chromosome from the mother (X) and the normal Y chromosome from the father (Y). In this case, the daughter would have normal vision because she has at least one normal color vision gene.

2. The daughter inherits the X chromosome with the color blindness gene from the mother (Xc) and the normal Y chromosome from the father (Y). In this case, she would be a carrier of color blindness, meaning she does not have the condition herself but can pass it on to her children if she has any.

The likelihood of a color-blind daughter in this scenario is low because both parents have normal vision. However, it is still possible due to the father inheriting the color blindness gene from his own father and passing it on to his daughter.

To accurately determine the occurrence of color blindness in the daughter, it would be best to consult with a medical professional who can conduct a thorough examination.