A normal man and a normal woman both having one of their parent...

Albinism is inherited in an autosomal recessive pattern that means both parents contribute a mutated gene for the person to have albinism. So, there is a $25 \%$ chance that any of their children will have albinism. Then $50 \%$ of the children will carry the mutated gene, but will not have albinism. The last possibility is to neither have albinism or carry the mutated gene, that's the other $25 \%$ chance.