Gene mutations are very common and can occur spontaneously or can be inherited. A gene is made up of the distinct characteristic of the father and the distinct characteristic of the mother, each carried in the DNA code in a single allele to make up the functional gene in the offspring. In other words, each gene has two alleles (one each from each parent). If the same trait is carried by both parents, the gene in the child is homozygous. When only one allele carries the trait, the gene is called heterozygous. This match up can have huge implications if an inherited gene has a mutation (like a SNP - pronounced SNIP) that produces a less effective enzyme for metabolizing an important nutrient like folate, choline or vitamin B12.