lesson
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Two brown-eyed parents can have a blue-eyed baby, even though neither parent has light eyes. The secret lies in the difference between the hidden code inside your cells and the traits that actually show up on the outside.
Genes and Alleles
You inherit two copies of every chromosome: one from each biological parent. A gene is a specific section of DNA that codes for a trait, while alleles are different versions of that same gene.
📊Interactive diagram
If alleles are the code inside your DNA, what do we call the visible traits that they build?
Genotype vs. Phenotype
Your genotype is the specific combination of alleles you carry in your DNA, written as letters like Bb. Your phenotype is the observable physical characteristic or trait produced by that genotype.
In the 1860s, Austrian monk Gregor Mendel discovered these inheritance rules by breeding thousands of pea plants and tracking how specific traits vanished and reappeared across generations.
📊Interactive diagram
When a cell contains two different alleles with conflicting instructions, how does it decide which trait appears in the phenotype?
Dominant and Recessive
A dominant allele is always expressed in the phenotype, even if you only inherit one copy (written as a capital letter, like B). A recessive allele is only expressed if you have two identical copies and no dominant allele present (written as a lowercase letter, like b).