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How many chromosomes do people have?
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Basics

How many chromosomes do people have?

In humans, each cell normally contains 23 pairs of chromosomes, totaling 46 chromosomes.

Chromosome Pairs

In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. These are categorized as follows:

  • Autosomes: Twenty-two of these pairs are called autosomes, which look the same in both males and females and are numbered by size.
  • Sex Chromosomes: The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome.

Karyotype

A picture of the human chromosomes lined up in pairs is called a karyotype. This visual representation is used by scientists and clinicians to organize and analyze the full set of chromosomes.

Frequently Asked Questions

Yes, some individuals have an extra chromosome (trisomy) and lead relatively normal lives, such as those with trisomy 21 (Down syndrome) who may have mild to moderate intellectual disability but can be independent with support. Other trisomies, like trisomy 18 or 13, are usually more severe and often result in serious health problems or early death. The effect of an extra chromosome varies widely by which chromosome is involved.
Prenatal chromosome testing is typically done by chorionic villus sampling (CVS) or amniocentesis, where fetal cells are collected and examined under a microscope to create a karyotype. More recently, non‑invasive prenatal testing (NIPT) analyzes fetal DNA fragments in the mother’s blood to screen for common aneuploidies (e.g., trisomy 21, 18, 13) without directly counting chromosomes.
Most nucleated cells in the body contain the full set of 46 chromosomes. Mature red blood cells, however, lose their nucleus during development and therefore have no chromosomes at all. Platelets and hair shafts also lack nuclei, so they do not contain chromosomes.
finding of 45 chromosomes usually indicates a missing chromosome (monosomy) or a structural abnormality such as a deletion. The clinical impact depends on which chromosome is affected; for example, Turner syndrome (45,X) can cause short stature and infertility, while loss of other chromosomes is often incompatible with life. A genetics professional can explain the specific implications and any needed monitoring or treatment.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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