Inheritance and Simple Genetics

Look around at a family. A child might have her mother's eyes, her father's smile, and her grandmother's curly hair. None of that is an accident. Living things pass instructions from one generation to the next, and those instructions decide a lot of what an organism looks like and how its body works. The study of how traits move from parents to offspring is called GENETICS.

Genes — The Instructions for Traits

Inside almost every cell of your body is a long, twisted molecule called DNA. Sections of DNA that carry the instructions for one specific TRAIT (like eye color or earlobe shape) are called GENES. Think of DNA as a giant cookbook, and each gene as a single recipe. You have around 20,000 of these recipes, and you got HALF of them from your biological mother and HALF from your biological father. That is why you look a bit like both of them.

1. TRAIT: a feature you can observe (eye color, hair type, blood type).
2. GENE: a section of DNA that carries the instructions for a trait.
3. ALLELE: one version of a gene (for example, the brown-eye allele or the blue-eye allele).
4. You inherit one allele from each parent for most traits — so two alleles per gene.

Dominant and Recessive Alleles

When the two alleles you get for a gene are DIFFERENT, one of them often wins. The winner is called DOMINANT and is written with a CAPITAL letter (B). The one that gets hidden is called RECESSIVE and is written with a lowercase letter (b). For eye color, the brown allele (B) is dominant and the blue allele (b) is recessive. If a child has BB she has brown eyes. If she has Bb she ALSO has brown eyes (the brown wins). She only has blue eyes if she has bb — two recessive alleles together. Recessive traits can stay hidden for generations and then show up again when two carriers have a child.

1. BB = two dominant alleles -> shows the dominant trait (brown eyes).
2. Bb = one of each -> still shows the dominant trait (brown eyes), but carries the recessive allele.
3. bb = two recessive alleles -> shows the recessive trait (blue eyes).

Inherited vs Acquired Traits

Not every feature of your body comes from your genes. Some things you are BORN with — your eye color, your blood type, the natural shape of your earlobes. These are INHERITED traits, written into your DNA before you were born. Other things you PICK UP through your life — a scar from falling off a bike, the language you speak, a tan from the summer sun, the ability to play piano. These are ACQUIRED traits. They come from experience, learning, the environment, or accidents — not from your genes. Acquired traits do NOT pass to your children. If you learn Spanish, your baby will not be born speaking Spanish.

Some Quick Examples

Inherited (in your DNA): eye color, hair color, blood type, attached or detached earlobes, having a widow's peak hairline, dimples, natural skin pigment, height tendency, curly vs straight hair. Acquired (during life): scars, tattoos, pierced ears, languages you speak, sports you play, instruments you play, riding a bike, a tan, scars from chickenpox, learning to read. A simple test: if you were locked alone in an empty room from birth, would you still have it? Eye color — yes (inherited). Riding a bike — no (acquired).