Inheritance Patterns of Ataxia
Each person inherits two copies of almost every gene, one from the mother and one from the father. (The exceptions are genes carried on the sex-determining chromosomes, X and Y.)
Some diseases develop when only one copy is mutated, even if the other is completely normal. Such a gene gives rise to the autosomal dominant inheritance pattern. A parent who has the mutation is probably affected by the disease. Each child of that parent has a 50% chance of inheriting the mutation, and thus developing the disease as well.
Other diseases develop only when both copies are mutated. This gives rise to the autosomal recessive inheritance pattern. Parents carrying one copy of the mutated gene are unaffected by the disease. Each parent must contribute one mutated gene to a child in order for the child to develop the disease. Each child has 25% chance of inheriting both mutations and developing the disease.