* A gene: A gene is a segment of DNA that codes for a specific trait, while a chromosome is a long strand of DNA that contains many genes.

* A protein: Proteins are the building blocks of cells and are made according to instructions encoded in DNA. They are not chromosomes themselves.

* A cell nucleus: The nucleus is the organelle within a cell that houses chromosomes, but it is not a chromosome itself.

* A cell membrane: The membrane surrounds a cell, providing structure and regulating what goes in and out. It has no relation to chromosomes.

* A mitochondria: Mitochondria are the powerhouses of the cell, responsible for energy production. They do not contain chromosomes.

In summary: Anything that is not a long, thread-like structure of DNA containing genetic information is not a chromosome.