By Mike Crystal – Updated Aug 30, 2022
Chromosomes are long strands of deoxyribonucleic acid (DNA) that reside in the nucleus of every animal and plant cell. They carry the genetic blueprints that dictate how an organism develops, functions, and reproduces. In humans, each body cell contains 23 pairs of chromosomes, totaling 46 individual chromosomes.
Every individual inherits one chromosome from each pair from each parent. This dual inheritance explains why we inherit traits—such as green eyes from a mother or dark hair from a father—through specific gene variants located on particular chromosomes. When two alleles differ, the dominant one typically expresses the observable trait.
In addition to the 22 pairs of autosomes, humans possess one pair of sex chromosomes. Females carry two X chromosomes (XX), while males carry one X and one Y (XY). The X chromosome is inherited from the mother in both sexes, whereas the Y chromosome comes exclusively from the father. All other chromosome pairs, the autosomes, are present in identical copies regardless of sex.
More complex organisms tend to have larger genomes and, consequently, more chromosomes. For example:
Because chromosome number is tightly linked to reproductive compatibility, individuals with differing chromosome counts rarely produce viable offspring. This constraint helps define species boundaries.
For further reading, consult the National Human Genome Research Institute or the American Society for Human Genetics.
