A gene is a recipe. But what does the recipe make, and how does that turn into a trait you can see, like brown fur?
Key idea
A gene holds the instructions for one protein. Proteins do the work of the cell: some are enzymes that speed up reactions (such as making a pigment), some build structures (such as hair and muscle), and some carry things (such as hemoglobin carrying oxygen). The trait comes from what the protein does.
Why it works
Proteins are chains of building blocks called amino acids. The order of the bases in a gene sets the order of the amino acids, and that order sets the protein's shape. Shape decides the job: an enzyme's shape lets it grab one molecule and change it. Change the gene and you can change the shape, the job, and so the trait.
Worked example: Gene to trait
Fur color in many mammals depends on an enzyme that helps make the dark pigment melanin. What would an animal look like if its copies of that gene made a protein that could not work?
- Gene → enzyme → pigment → fur color.
- If the enzyme does not work, little or no dark pigment is made.
Answer: Very light or white fur (and often pale eyes): this is albinism.
Worked example: Read the chain
In the visual, the DNA template TAC AAA CCG ATT is copied as AUG UUU GGC UAA. What does each codon mean?
- AUG means "start" and adds Met.
- UUU adds Phe; GGC adds Gly.
- UAA means "stop".
Answer: The protein chain is Met–Phe–Gly.
Common mistake
Students think a gene is a tiny trait, as if a "blue eye" were stored in the cell. A gene is a set of instructions for a protein. The trait appears only when the protein does its job, for example by making more or less pigment.