Highlight from 'Visual Thinking' by Temple Grandin

Most of our traits are polygenic, which means they are affected by many genes. Another mechanism for understanding individual difference is single-nucleotide polymorphisms, or SNPs. Each one of these refers to possible substitutions at a single rung on the ladder of DNA. Sometimes a rung on the ladder changes and nobody knows why. This is called a de novo mutation and occurs in a small percentage of people diagnosed with autism.