Here's why:

* Sex chromosomes: Humans have two sex chromosomes: X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

* Gene location: Some genes are located specifically on the X chromosome. These genes are called X-linked genes.

* Inheritance pattern: Because males only have one X chromosome, they inherit X-linked traits directly from their mothers. Females inherit one X chromosome from their mother and one from their father.

Mendelian traits are traits controlled by a single gene with two alleles, following the principles of Mendelian inheritance. While some Mendelian traits can be located on the X chromosome (making them sex-linked), the term "Mendelian trait" doesn't specifically refer to the chromosome location.

In summary:

* Sex-linked traits are specifically linked to the X chromosome and exhibit unique inheritance patterns due to the sex chromosomes.

* Mendelian traits can be located on any chromosome, including the X chromosome. If they are on the X chromosome, they become sex-linked.

Let me know if you'd like more details on sex-linked inheritance or examples of X-linked traits!