In humans, aniridia (the absence of the iris, the colored part of the eye) can be a genetically determined cause of blindness that is transmitted as a dominant trait. Unilateral deafness (total deafness in one ear) can also be genetically determined and has a dominant pattern of inheritance. A man with genetically determined aniridia whose mother is not blind marries a woman with genetically determined unilateral deafness whose father has normal hearing. What proportion of their children would be expected to be both blind and deaf in one ear?
