1. Largest chromosome. Carries the most genes (about 2,000), involved in brain development, vision, hearing, muscle function, and countless everyday cellular processes.

2. Formed by the fusion of two ancestral ape chromosomes. Contains genes involved in brain development and normal growth.

3. Contains genes involved in kidney development, vision, and cell growth, including the VHL gene.

4. Contains genes important for brain and muscle function, including the HTT gene associated with Huntington's disease.

5. Contains genes involved in embryonic development, lung function, and digestion, including the APC gene, which helps suppress tumors.

6. Home to the HLA region, which helps your immune system recognize viruses and bacteria and makes organ transplant matching possible.

7. Contains genes involved in lung function, hearing, and taste, including CFTR, associated with cystic fibrosis.

8. Contains genes involved in cell growth, skeletal development, and normal tissue repair, including MYC, an important regulator of cell growth.

9. Contains the ABO gene that determines your blood type, along with genes involved in DNA repair and cell division.

10. Contains genes involved in nerve development and hormone signaling, including RET, which guides the development of parts of the nervous system.

11. Contains the INS gene, which produces insulin, along with genes involved in smell and blood cell development.

12. Contains genes involved in metabolism, vitamin processing, and brain development, including PAH, associated with phenylketonuria.

13. Contains genes important for normal DNA repair, eye development, and cell division, including BRCA2.

14. Contains genes that help produce antibodies, making it an essential chromosome for the immune system.

15. Contains genes involved in brain development, sleep regulation, and growth. Changes in this chromosome can lead to Prader-Willi or Angelman syndromes.

16. Contains genes important for kidney function, metabolism, and blood pressure regulation, including PKD1.

17. Contains BRCA1 and TP53, one of the body's most important tumor-suppressor genes, along with many genes involved in brain and nerve function.

18. Contains genes involved in embryonic development and muscle formation. Although it carries fewer genes than many chromosomes, they are essential.

19. Most gene-dense chromosome. Rich in genes involved in cholesterol metabolism, immune function, and cell communication.

20. Contains genes involved in pancreatic function, metabolism, and normal brain development.

21. Smallest numbered chromosome. Contains genes involved in brain and immune development. An extra copy causes Down syndrome.

22. Contains genes involved in brain development, heart development, and immune function. 

X. Carries hundreds of genes involved in vision, blood clotting, muscle function, reproduction, and brain development.

Y. Contains genes that initiate male development and support sperm production and fertility.