Basic unit of heredity.

**The reasoning** Think of heredity like a recipe book being passed from parents to children. The **gene** is the actual recipe – the specific instruction for one trait, like eye color or blood type. It's the smallest functional unit that carries information from one generation to the next. Genes are made of DNA and tell your body how to make proteins, which determine your characteristics. **Why the wrong options tempt you** - **Cell** – This is the basic unit of *life*, not heredity. Yes, cells contain genetic material, but they're too big and do too many things to be the basic heredity unit. - **Chromosome** – This is like the chapter in the recipe book; it's a collection of *many* genes bundled together. It carries genes but isn't the basic unit itself. - **Nucleus** – This is just the kitchen where the recipe book is stored. It *houses* chromosomes and genes but isn't the unit of heredity. **Quick takeaway** Gene = one instruction, one trait; it's the *smallest* piece of hereditary information that can be passed down – that's what makes it the **basic** unit.