Here's why:

* Alleles: Different versions of a gene.

* Linkage: When genes are located close together on the same chromosome, they tend to be inherited together. This is because during meiosis (cell division that produces gametes), the chromosomes exchange genetic material (crossing over). However, genes that are very close together are less likely to be separated by crossing over.

Example:

Imagine two genes, one for hair color (brown or blonde) and another for eye color (blue or brown). If these genes are linked on the same chromosome, someone with brown hair is more likely to also have brown eyes, simply because these genes are inherited as a unit.

Important Note: Linkage is not absolute. While linked genes are more likely to be inherited together, crossing over can still occur, leading to recombination of alleles. The closer the genes are, the less likely they are to recombine.