How many chromosomes do humans have: 46, and what that means

What to expect in this article

1. The number and why they occur in pairs
2. Autosomes and sex chromosomes
3. What a chromosome contains
4. How many genes that is
5. Why you have two copies of every gene
6. Three misconceptions about chromosomes and genes
7. What a DNA test reads from this
8. What a DNA test cannot do
9. What matters in the end
Frequently asked questions
Sources

The number and why they occur in pairs

The answer is clear and appears in every genetics textbook. MedlinePlus Genetics, the information resource of the U.S. National Library of Medicine, puts it this way:

In English: In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. The quotation appears in the English original because the source is in English—the translation is ours.

Why pairs instead of 46 individual chromosomes

The arrangement in pairs is not an organizational scheme but a biological fact. Each pair consists of two chromosomes with the same function—one comes from the mother and one from the father.

This leads to the structure of the entire genome: Everything located on one chromosome is also present in corresponding form on its partner chromosome. Humans therefore have two copies of almost every piece of genetic information.

That is why traits are not simply added together but combined. Which of the two versions prevails, or whether both work together, is the real question of heredity—and it arises 23 times in parallel.

The word “normally” is there intentionally

The quoted wording contains a qualification that is easy to overlook: normally. It is not a linguistic softener but a technical clarification.

There are deviations from the number 46, and they are generally medically significant. Such questions belong in genetic counseling and cannot be resolved either by an article or by a standard consumer DNA test.

For the usual case, the figure applies without exception: 46 chromosomes, regardless of ancestry, sex, or age. There is no population group that systematically has more or fewer.

Why the number is sometimes different online

Occasionally, you may read that humans have 23 rather than 46 chromosomes. Both figures can be correct; they simply refer to different cell types.

Ordinary body cells contain the diploid set, that is, 46. Egg and sperm cells contain the haploid set of 23 chromosomes—only then can their union produce 46 again rather than 92.

When people ask how many chromosomes humans have, they almost always mean a body cell. The answer is 46.

Autosomes and sex chromosomes

Not all 23 pairs are structured the same way. MedlinePlus distinguishes between two groups, and this distinction explains a large part of what people want to know about genetics.

Information based on MedlinePlus Genetics, U.S. National Library of Medicine (NLM), as of 2021. The proportions in the last row were calculated from this information.

Numbering the autosomes by size is a practical convention: Chromosome 1 is the largest, and Chromosome 22 is one of the smallest. The order has nothing to do with the significance of the genes they contain.

The letters X and Y are also merely designations and do not describe the shape. They became established historically and are still used today, although they say nothing about the structure of the two chromosomes.

How sex is determined

The distribution of X and Y leads to a rule that surprises many people. Because women carry two X chromosomes, they always pass on an X. Men carry one X and one Y and pass on either one or the other.

A child's chromosomal sex is therefore determined on the father's side. If the father contributes an X, it combines with the mother's X to produce the XX combination; if he contributes a Y, the result is XY.

Important for context: This is a statement about chromosomes, not gender identity. The two levels coincide for most people, but they are not the same—and the number of chromosomes says nothing about this.

What a chromosome contains

A chromosome is a form of packaging. It consists of DNA wound up inside a cell so that it can fit at all and be distributed properly during cell division.

Genes lie on this DNA. MedlinePlus states that each chromosome contains many genes and that genes consist of DNA (as of 2024). The three terms therefore do not exist side by side but within one another: DNA is the material, genes are sections of it, and chromosomes are the packages.

How large a gene is

Genes vary greatly in length. MedlinePlus gives the range as extending from a few hundred DNA base pairs to more than two million base pairs (as of 2024).

The factor between the shortest and longest gene is therefore in the thousands. This is one reason why the number of genes cannot simply be inferred from the size of a chromosome.

Why chromosome size reveals little

The autosomes are numbered by size, from 1 as the largest to 22 as one of the smallest. This might suggest that chromosome 1 also carries the most genes and chromosome 22 the fewest.

This assumption is too simplistic, and the reason is given in the previous section: genes vary in length. If a single gene can range from a few hundred to more than two million base pairs, the length of a chromosome segment says nothing reliable about the number of genes it contains.

In addition, not every segment of DNA belongs to a gene. Between genes are regions that have other functions or whose role has not yet been fully clarified. The source material used here does not indicate exactly how large this share is.

Not every gene makes a protein

The widespread notion that every gene is an instruction manual for a protein is too simplistic. MedlinePlus explains that some genes provide instructions for making proteins, while others do not code for proteins and instead help regulate other genes (as of 2024).

This regulatory function is why the sheer number of genes says little about the complexity of an organism. What matters is not only which blueprints are present, but also when and how strongly they are read.

A metaphor that holds up—and one that does not

For the relationship between DNA, genes, and chromosomes, there is an image that accurately captures the connection: DNA is the text, a gene is a chapter in it, and a chromosome is the volume in which several chapters are bound together. Humans have 46 such volumes, in 23 pairs.

A metaphor that does not hold up is the blueprint. It suggests that somewhere there is a finished drawing of a human being that only needs to be followed. In reality, the genetic material does not describe a final form; it provides instructions and regulatory signals whose effects depend on circumstances.

The difference sounds like quibbling, but it is not. Anyone who understands the genetic material as a blueprint expects a genetic test to make predictions. Anyone who understands it as a collection of instructions expects clues—and that is the expectation consistent with what such tests can deliver.

How many genes there are

The number of chromosomes has long been established. The number of genes was different for a long time, and the correction of these estimates is one of the most remarkable turns in modern genetics.

Source: MedlinePlus Genetics, U.S. National Library of Medicine (NLM), as of 2021 and 2024

From 100,000 to 20,000

The Human Genome Project ran from 1990 to 2003 and estimated that humans had 20,000 to 25,000 genes. According to more recent findings, the human genome contains around 19,900 genes used to produce proteins (MedlinePlus, as of 2024).

Before the project, estimates were significantly higher—in many textbooks and media reports, the figure was around 100,000 genes. The actual number of genes is about one-fifth of what was estimated before the Human Genome Project.

This correction is more than a footnote. It overturned the idea that every trait and every disease has a gene responsible for it—there simply are not enough genes for that.

What the lower number means in practical terms

The revision from 100,000 to around 20,000 changed how people thought about genetics. As long as scientists were working with six-figure gene counts, it seemed plausible that every trait and every disease had a gene responsible for it.

With around 19,900 protein-coding genes, this calculation no longer adds up. Humans have more distinguishable traits, metabolic pathways, and regulatory circuits than they have genes.

Part of the explanation lies in the genes that MedlinePlus describes as non-protein-coding and that regulate other genes. A single gene can therefore act in very different places, depending on when and how strongly it is read.

For evaluating genetic tests, this calls for healthy skepticism toward simple associations. Statements such as “this gene determines that trait” are rarely as unambiguous as they sound.

Why you have two copies of each gene

The arrangement in pairs leads to a rule that MedlinePlus describes as follows: people generally inherit two copies of each gene, one from each parent (as of 2024).

The two copies do not have to be identical. Different forms of the same gene are called alleles, and according to MedlinePlus, they contribute to a person’s unique physical characteristics.

This explains why siblings with the same parents can look different. Each child receives their own combination of the two versions from each parent—and across 23 pairs, that results in a very large number of possible combinations.

The exception: the 23rd pair

In men, the two-copy rule does not apply in the same way to the pair of sex chromosomes. Because X and Y are structured differently, genes on the X chromosome are present only once in men.

This explains why certain traits occur more often in men than in women: the second copy that could compensate for a variation is missing. According to MedlinePlus, women carry two copies of the X chromosome and have this reserve.

What alleles mean in everyday life

The term allele sounds academic, but it describes precisely what every DNA test is about. An allele is one of the possible forms of a gene—and because you have two copies of each gene, you carry either two identical copies or two different ones.

Those are exactly the differences a DNA test reads. The information is not the gene itself, but which variant of it you have. At the vast majority of positions in the genome, all humans are the same anyway.

That is why a test does not need to read the entire genome to say something meaningful. It examines the positions where humans are known to differ—which we’ll get to in a moment.

At the same time, this is also the reason for one limitation: A test only finds what it is looking for. A variant at a position outside the scope of the test remains undetected—regardless of how significant it might be.

Why Siblings Differ

The 23 pairs are reshuffled when egg and sperm cells are formed. Each pair passes on one of its two members, and which one it is is determined independently for each pair.

This distribution alone results in millions of possible combinations from each parent. Except in the case of identical twins, it is practically impossible for two siblings to receive the same combination.

That is why a family member’s test result says only so much about the others. Siblings share a large portion of their genetic material, but not the same set of variants—and those variants are exactly what a DNA test reads.

Three Misconceptions About Chromosomes and Genes

What a DNA Test Reads

The third point in the table deserves a more detailed explanation because it is often blurred in the market. A standard commercial DNA test does not read all 46 chromosomes from beginning to end.

Instead, it examines specific, predefined positions in the genetic material—so-called SNPs, meaning positions at which people are known to differ. mybody®x (MYBODY Lab GmbH) works with more than 700,000 such positions.

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It examines over 170 genetic variations and provides 74 reports in twelve chapters across approximately 240 pages. What the test does not do: It does not count chromosomes or detect chromosomal abnormalities—it is not designed for that. It does not diagnose, predict illness, or replace a medical examination. Method: SNP genotyping at over 700,000 individual positions, not whole-genome sequencing.

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More than 700,000 positions are not a weak offering—it is simply a different method from reading the entire genome. The difference needs to be stated because marketing often blurs it.

Why SNP genotyping is sufficient for this purpose

The reason lies in what was stated about alleles in the previous chapter: At the vast majority of positions in the genome, people do not differ. A method that specifically examines the variable sites therefore omits information that would not be relevant to the question anyway.

For nutritional and lifestyle counseling, this is a sensible scope. For medical questions—such as rare variants or chromosomal abnormalities—it is the wrong approach, and these tests are not designed for that purpose.

The honest wording is therefore not “we read your DNA,” but “we examine more than 700,000 positions at which people differ.” That is more precise and defensible.

Regarding data handling: The saliva sample and DNA sequence are completely destroyed two months after the analysis is completed; the samples are pseudonymized, and transmission is SSL-encrypted.

All pricing and service information is current as of August 5, 2026. Prices and the scope of services may change; the respective product page is always authoritative.

What a DNA test cannot do

The first limitation follows directly from the method. Anyone who wants to know whether their chromosome count differs from the norm needs a different examination. That is a question for human genetics and belongs in the hands of a physician.

The second limitation concerns the claim being made. DNA analysis is used for nutritional and lifestyle counseling. It is not a diagnostic procedure, does not predict disease, and does not replace a medical examination or consultation.

The third limitation is the most realistic expectation of the benefits. In 2022, the DGE concluded that gene, blood, and microbiome analyses generally did not produce statistically verifiable improvements in dietary behavior, although it did note moderate effects from increased motivation.

And a fourth point related to the subject of this article: No test is needed to answer the question of how many chromosomes humans have. The answer is 46; it applies to everyone and is freely available in every reputable genetics reference.

What happens to your data

With a topic like this, the question of data handling is part of the discussion, even if it was not asked. At mybody®x, the saliva sample and DNA sequence are completely destroyed two months after the analysis is completed.

The samples are processed using pseudonyms, transmitted with SSL encryption, and analyzed in an ISO-certified laboratory in Germany. Anyone who asks what happens to the data receives a specific answer rather than a general assurance.

This is not a minor detail. Genetic data are particularly sensitive because they cannot be changed and because, in part, they also reveal information about relatives. An Anbieter that makes no clear statement on this point should not be chosen.

What ultimately matters

46 chromosomes in 23 pairs, including 22 pairs of autosomes and one pair of sex chromosomes—that is the answer, and it does not change.

What follows from this is more interesting. Around 19,900 protein-coding genes are fewer than was long assumed, and each is present in two copies. Together, these facts explain why inheritance cannot be represented in simple lists of traits.

And a third point that extends beyond the topic: The number of chromosomes is the same in all humans. What distinguishes people genetically are variants at individual positions—a very small part of the genetic material that nevertheless makes all the difference.

This leads to a useful rule of thumb for evaluating genetic tests. The simpler the classification an Anbieter promises sounds, the more closely it is worth looking at what it is based on. With around 19,900 protein-coding genes and genes that regulate other genes, simple one-to-one statements are the exception.

The second question that is always worth asking concerns the method. Whether a test reads the genome in its entirety or examines specific individual positions is a fundamental difference—and it determines which questions the test can answer at all.

Your specific next step: If you are interested in the topic beyond the number, see how the difference between DNA, a gene, and a chromosome is explained in our article on the structure of DNA. And if you are interested in a DNA test, first check which method it uses—that is the question that makes the difference.

Frequently asked questions

Sources

1. MedlinePlus Genetics, U.S. National Library of Medicine (NLM): How many chromosomes do people have?, as of 2021 — medlineplus.gov
2. MedlinePlus Genetics, U.S. National Library of Medicine (NLM): What is a gene?, as of 2024 — medlineplus.gov

The number of chromosomes, their division into 22 pairs of autosomes and one pair of sex chromosomes, their numbering by size, and the references to X and Y are based on source [1]. The definition of a gene, the gene counts from the Human Genome Project, and the more recent figure of around 19,900 protein-coding genes, the range of gene lengths, the ratio of genes to DNA and chromosomes, as well as the two-copy rule and the term allele, come from source [2]. The quotation in Chapter 1 appears in the original English; the German version in the body text below is our translation. Information about the procedures, scope, and data protection of mybody®x tests comes from the product pages and the knowledge base, accessed on August 5, 2026.

mybody®x Editorial & Expert Team

Genetics Nutrigenetics Science Communication

This article was written and professionally reviewed by the mybody®x Editorial and Expert Team. The team combines expertise in nutrigenetics, microbiome and gut science, blood analysis interpretation, nutritional science, and laboratory diagnostics.

Published on August 5, 2026 · Last updated on August 5, 2026

Medical notice: This article is intended for general information and does not replace medical advice, diagnosis, or treatment. Questions about chromosomal disorders, having children, or hereditary diseases should be addressed in genetic counseling; mybody®x DNA analysis is intended for nutrition and lifestyle advice and is not a diagnostic procedure.