While some traits are influenced by a single gene, most traits are controlled by **multiple genes** working together (polygenic inheritance). Characteristics like height, skin tone, and body weight are classic examples. Understanding this helps explain why traits often show continuous variation rather than simple, clear-cut categories.

Dominance only refers to how alleles express themselves in a heterozygous condition. It has no connection to how frequent a trait is. A dominant trait (like polydactyly, or extra fingers/toes) can be rare, and a recessive trait (like straight hair) can be common, depending entirely on allele frequency in a population.

This is one of the most persistent **genetics myths**. Genes provide biological instructions, but the **environment strongly influences** how these instructions are expressed. Factors like nutrition, education, lifestyle, and surroundings interact with genetic makeup. This interaction explains why individuals with similar genetic backgrounds (e.g., twins) can still show noticeable differences.

A mutation is simply a change in DNA sequence. Some mutations are harmful, many have no effect (neutral), and a few can be beneficial (leading to adaptation). Mutations are essential for genetic variation and play a crucial role in evolution. Without them, populations would lack the diversity needed to adapt to changing environments.

Some genetic conditions are inherited, but others result from **new mutations** that occur spontaneously during the formation of gametes (sperm/egg) or early embryonic development. This distinction is important when studying inheritance patterns and counseling families.

DNA is the *molecule* that stores the entire genetic information (the entire instruction book). **Genes** are specific *segments* of DNA that contain instructions for making proteins or functional RNA (individual chapters or paragraphs). In simple terms, genes are parts of DNA, but they are not identical to the whole molecule.

**Genetics** applies to all living organisms—plants, bacteria, animals, and fungi. Much of modern genetic knowledge comes from studies on simpler organisms (like fruit flies and bacteria). Research on these model organisms has helped scientists understand complex biological processes, demonstrating the universality of genetic principles.