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How Many Chromosomes Do Humans Have?
Updated on September 20, 2022
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How Many Chromosomes Do Humans Have?

Human chromosomes come in pairs. We normally have 46 chromosomes or 23 pairs. 22 of these pairs (called autosomes) are the same in both sexes. 

The 23rd pair is different for males and females. They are called sex chromosomes because they determine our sex. 

Females have two X chromosomes, while males have one X and Y chromosomes.1

How Many Chromosomes Do Humans Have? 2

Do All Humans Have 23 Pairs of Chromosomes?

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

What is a Chromosome?

Chromosomes are like threads inside the nucleus of your cells. Each chromosome contains deoxyribonucleic acid (DNA) and proteins to help stabilize it.

Chromosomes are your biological building blocks. They have an entire chain of DNA. Each pair of chromosomes contain our genome or genetic material. 

Our chromosomes are passed to us from our parents during conception. Half of them come from our mothers and the other half from our fathers. 

This is why you inherit some characteristics from your father and others from your mother.

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How Do Chromosomes Make You Unique?

The genetic data inside your chromosomes play an important role in making you who you are. But how does it make each person different? 

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 makes 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.

Hereditary Mutation

Hereditary mutations are abnormal changes in a person’s DNA. They are present from the time you are conceived and exist in every cell of your body.

Research shows parents pass about 60 percent of genetic mutations to their offspring.2 Some of them (like heterochromia) aren’t harmful and give you a unique appearance.

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. 

It is 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:

Monosomy

When a person has one less chromosome present, it is monosomy. In this case, one particular chromosome was 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

It’s 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.

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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Resources

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  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 studied B.S. Psychology and enjoys writing about health and wellness.
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