The way that a genetic condition is passed from parents to their children is called an INHERITANCE PATTERN. SCA27B has an AUTOSOMAL DOMINANT inheritance pattern with a few extra rules. 

Recall from the "What is a gene?" page that we have 2 copies of most genes in each cell of the body. One copy is passed down (inherited) from each parent. In an autosomal dominant condition, 1 of the 2 gene copies has a pathogenic (disease-causing) variant that makes that copy not work as expected or not work at all. Having 1 out of the 2 gene copies not working correctly is enough to cause the disease. 

You can think of the 2 copies of the gene like the 2 wheels on a bike. If just 1 of the 2 wheels is damaged, the bike will not work anymore. The bike can't function with only one working wheel. If just 1 of the 2 copies of a gene is not working for an autosomal dominant condition, the cells can't function normally.

This all means that in every pregnancy between the couple shown below, there is a 50% (1 in 2) chance that the parent with a pathogenic (disease-causing) variant will pass on the copy of the gene with the pathogenic variant and therefore have an affected child. This also means that there is a 50% (1 in 2) chance that the parent with a pathogenic variant will pass on the normal copy of the gene. 

In most autosomal dominant conditions, it does not matter if the pathogenic variant comes from the male or the female parent. This is not true for SCA27B.