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Facts About Human Chromosomes
Updated on February 7, 2024
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Facts About Human Chromosomes

Humans typically have 46 chromosomes, divided into 23 pairs.

Twenty-two of these pairs (called autosomes) are the same in both sexes. The 23rd pair is what determines our biological sexes, called sex chromosomes. Those assigned female at birth have two X chromosomes, while those assigned male at birth have one X and Y chromosome.1

Facts About Human Chromosomes 6

What is a Chromosome?

Chromosomes are thread-like structures compacted into your nucleus and are considered your biological building blocks. They have an entire double-helix deoxyribonucleic acid (DNA) chain, which contains the unique instructions that contribute to who you are. Each pair of chromosomes contains our genome or genetic material.

Our chromosomes are passed to us from our parents during conception through our reproductive cells. Half come from our mothers, and the other half from our fathers when the sperm cell fertilizes the egg.

Our genetic material is a distinctive combination of our parents' and dictates how we look, what we may be genetically predisposed to, and even key personality traits.

Your pair of sex chromosomes are special as they dictate your sex at birth.

Image of Chromosomes

Do Humans Have 23 or 46 Chromosomes?

Humans have 46 chromosomes that are paired up, which makes 23 pairs. Human beings do not have 23 chromosomes.

Do All Humans Have 23 Pairs of Chromosomes?

Humans typically have 23 pairs of chromosomes. However, some people undergo genetic changes affecting their chromosomes, development, and growth.

Some people may develop mutations in either the number of chromosomes or the structure of chromosomes when their cells are dividing. These mutations can lead to birth defects, intellectual disabilities, genetic conditions, or other significant developmental differences. An extra chromosome, a structurally unsound chromosome, or a missing chromosome can impact your growth.

For example, if you accidentally develop an extra copy of chromosome 21, you may develop Down Syndrome. Any extra copy of a chromosome is called a trisomy, which is why you'll often hear Down Syndrome being referred to as Trisomy 21.

Other trisomy conditions and potential consequences of an extra chromosome include:

  • Trisomy 13 or Patau Syndrome
  • Trisomy 18 or Edward Syndrome

Do Men and Women Have Different Numbers of Chromosomes?

No, men and women have the same number of chromosomes—46 in all, in 23 pairs. The only difference is in the sex chromosomes, as those assigned female at birth will have two X chromosomes (denoted as XX), and those assigned male at birth will have one X and one Y chromosome (denoted as XY).

Facts About Human Chromosomes 7
source: 123rf

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How Do Chromosomes Make You Unique?

The genetic data inside your chromosomes are full of information from both parents and, when they come together, contribute to your unique personhood. You may receive physical traits from your mother and father that build your unique physical appearance or even health predispositions that may make up your distinct constitution.

The genes in your DNA are expressed differently depending on how dominant they are. So, while your parents may have different hair colors, the more dominant color is more likely to be expressed. This is why many people often look like a mix of their parents' physical traits.

Hereditary Traits

Chromosomes carry hereditary information. This information determines many things about you, including how you look and how your body will react to its environment. 

There are approximately 24,000 genes or genetic information contained within your 46 chromosomes. They’re what make you different from everyone else.

One example of an inherited trait is your eye color. If both your parents have brown eyes and you have brown eyes, it’s because they passed those genes to you.

Parents carry different genes, and there’s no telling which DNA they’ll pass on to you. This makes your physical appearance and behavioral traits different from others, even your siblings.

Facts About Human Chromosomes 8

Hereditary Mutations

Hereditary mutations are abnormal changes in a person’s DNA, which may also make you more unique. They are present from the time you are conceived and exist in every single cell of your body.

Not only did you inherit a hodgepodge of genes from your parents as is, but any mutation would change that mix even further.

Research shows parents pass about 60 percent of genetic mutations to their offspring.2 Some of them (like heterochromia) aren’t harmful and just make you physically stand out.

However, certain genetic mutations increase your risk for diseases and various health conditions. Sickle cell anemia and cystic fibrosis are some examples.

Acquired Mutation

Acquired mutations occur after you are born. They aren’t present at conception. 

They're only present in specific cells and can develop from unexpected cell division or environmental factors. The most common causes of acquired gene mutations are:

  • Cigarette smoking
  • Exposure to radiation
  • Unhealthy diet
  • Hormonal imbalances

It’s also possible for mutations to occur randomly when human cells divide.

Chromosomal Abnormalities

Chromosome abnormalities can occur during conception, early fetal development, or after birth. This is the most common cause of genetic disorders.

Some chromosomal abnormalities happen when there’s an excess chromosome or a section of it is duplicated or deleted.3

A change in the usual number of chromosomes is called aneuploidy.4 There are many types of aneuploidies. Below are some of them:

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Monosomy

When a person has one fewer chromosome present, it is monosomy. In this case, one particular chromosome was only copied once.

One of the most common types of monosomy is Turner Syndrome. This condition affects women and causes them to have a single copy of the X chromosome.

In some cases, a person might have a complete extra set of chromosomes present or two additional sets of chromosomes.

Trisomy

This is the most common type of aneuploidy. People with trisomy have an extra copy of one particular chromosome in each cell. 

For example, when there’s an extra copy of chromosome 21, the person is diagnosed with trisomy 21 or Down Syndrome.

Mosaicism

There are also cases where an individual has two or more cell populations with different genetic makeup. This is chromosomal mosaicism.

An error in cell division causes chromosomal mosaicism. Some cells end up with one additional or one missing chromosome.

People with mosaicism may have 45 or 47 chromosomes in a cell. Mosaic Turner Syndrome is an example of chromosomal mosaicism.

Women with Mosaic Turner Syndrome have 45 chromosomes in some of their cells. Some of them are missing one copy of the X chromosome, but others aren’t.

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Cell Mutation and Cancer

Many types of cancer occur because of changes in the number of chromosomes in cells. They occur in non-egg or non-sperm cells called somatic cells.

These genetic changes are not inherited. They develop as the cancerous tumor forms or spreads. 

According to the American Cancer Society, there needs to be more than one mutation in a cell for cancer to develop. However, your cancer risk is higher when you inherit an abnormal gene copy from your parents.5

Cells start with one mutation. So, having multiple mutations may cause cancers to develop faster. Gene mutations occur throughout your life. In most cases, these acquired mutations cause cancer. 

Most of the time, your body’s cells detect unusual changes and will attempt to repair them. When repair doesn’t occur, the cells will die. This is known as apoptosis.

But if the cell survives an unusual change, it may lead to a person developing cancer.

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Updated on February 7, 2024
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5 sources cited
Updated on February 7, 2024
  1. Chromosome Map.” National Center for Biotechnology Information.
  2. How Many Genetic Mutations Do I Have?” Live Science.
  3. Chromosomal problems in newborn babies.” About Kids Health.
  4. Chromosomal Abnormalities.” Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals.
  5. Changes in Genes.” American Cancer Society.
Dr. Dhingra
Dr. Harshi Dhingra
Medical Reviewer
Dr Harshi Dhingra is a licensed medical doctor with a specialization in Pathology. Dr. Dhingra has of over a decade in diagnostic, clinical, research and teaching work, including managing all sections of Pathology laboratory including histopathology, cytology, hematology and clinical Pathology.
Cristine Santander
Cristine Santander
Content Contributor
Cristine Santander is a content writer for KnowYourDNA. She has a B.S. in Psychology and enjoys writing about health and wellness.
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