6. Mutations, Pedigrees & Reading Genetic Data

A mutation is a change in the DNA sequence. Its effect depends on where it happens: some mutations are neutral (no real effect), some are harmful, and a few are helpful in a particular environment. A mutation in a sex cell can be passed to offspring; a mutation in an ordinary body cell usually affects only that individual.

A pedigree chart tracks a trait through a family. Squares are males, circles are females, and shaded symbols mark individuals who have the trait. A classic clue: if two unaffected parents have a child who is affected, the trait is most likely recessive (both parents were carriers).

Traits aren't always set by genes alone — environment matters too. Nutrition, temperature, and sunlight can all influence a phenotype, so genes and environment often work together.

Reading genetic data (a GED® skill). Items may give a Punnett square, a ratio, or a pedigree and ask what it shows. Track exactly who is affected, use the legend, and conclude only what the data supports. And remember: correlation is not causation.

⚠️ Common misconception: not every mutation is harmful. A mutation is simply a DNA change — its effect can be neutral, harmful, or helpful.

💡 Tip: for a pedigree, find who has the trait, then ask which genotypes are possible — two unaffected parents with an affected child points to a recessive trait.

📚 Sources: OpenStax Biology / Concepts of Biology; Campbell & Reece, Biology; NHGRI / NIH; MedlinePlus Genetics; Mendel's laws.