Final answer:
DISC1 is linked to psychiatric conditions such as schizophrenia; disorders like Huntington's demonstrate how autosomal dominant patterns require only one faulty gene for disease expression, potentially manifesting later in life and being passed to offspring. Disease genes arise due to mutations or hereditary transmission.
Step-by-step explanation:
DISC1 is associated with a range of psychiatric conditions, including schizophrenia, bipolar disorder, and depression. Disorders like Huntington's disease illustrate how a dominant allele of a single gene on an autosome can lead to genetic disorders. Unlike autosomal recessive disorders, where two copies of the recessive allele are needed to express the disease, autosomal dominant disorders require only one copy of the faulty gene to manifest. Individuals with such disorders often know they carry the gene, but symptoms can appear later in life, potentially after having children, hence passing on the gene to the next generation.
Various mechanisms can lead to the development of a disease gene. Mutations can occur spontaneously due to errors during cell division or be induced by environmental factors. Another way a disease gene comes to be is through inheritance from a parent who carries a mutant gene. When discussing genetic inheritance patterns and the passing of genetic disorders from parents to children, Punnett squares are often used to predict the likelihood of inheriting a particular disorder.