Type the correct answer in the box. Use numerals instead of words. A recessive gene located on the X chromosome is the cause of one type of colorblindness (denoted by X^c). Let the genotype for normal vision be
denoted by X^+.
Suppose a mother with normal vision (X^+X^c) and a father with normal vision (X^+Y) reproduce. Their child's possible genotypes can be illustrated
with the following Punnett square.

If they have a son, his chance of having this type of colorblindness is [ Blank ] %.