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How Many Chromosomes Do Humans Have?

Updated on: July 2, 2021
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Most humans have 46 chromosomes. Human chromosomes come in pairs, so there are 23 pairs of chromosomes.

All beings have chromosomes, but not all of them have the same total number of chromosomes. For example, while humans have 23 pairs of chromosomes, potatoes and gorillas have 48 individual chromosomes, while rattlesnakes have 184 chromosomes. Plant cells, on the other hand, have a different number of chromosomes.

Keep in mind that the number of chromosomes does not correlate with the organism's complexity, and it’s impossible to distinguish a species through the number of chromosomes alone. However, the genetic material inside each chromosome does affect the complexity of a species.

The number of chromosomes a species has is completely random and can change over time. Some scientists believe that a random “sticking together” of chromosomes is what caused the evolution from primate to human.

What is a Chromosome?

Chromosomes are biological building blocks. Each contains a chain of DNA with the code that makes an individual who they are in terms of their genetic makeup.

How Many Chromosomes Do Humans Have? 1

Our chromosomes are passed to us from our parents during conception. Half come from our mothers and a half from our fathers. This is the reason why children inherit some characteristics from their father and others from their mother. Chromosomes contain our genome or genetic material, which is written across each pair of chromosomes. 

Chromosomes contain our DNA code and are home to our entire genetic sequence. The information stored within your chromosomes is what makes you an individual.


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How Do Chromosomes Make Each Being Distinctly Unique?

How is it that the information within our chromosomes plays an important role in making each being who or what it is?

We are who we are, genetically speaking, due to gene mutations. Mutations are permanent changes in a piece of DNA and occur in one of two ways.

Hereditary Mutation

Hereditary mutations are those passed on from the mother and father. These mutations are present from the time you are conceived and exist in every cell of your body.

One excellent example is your eye color. If your parents had brown eyes and you have brown eyes, it’s because of your genes, and you’ll pass that along to any child you conceive.

Research shows parents pass about 60 percent of gene mutations to their offspring. And because that 60 percent varies between parents, it’s what makes each person different, even when they are siblings.

Acquired Mutation

The other type of gene mutation is the acquired mutation. This type of mutation occurs during your life. It isn’t present at conception. It is only present in certain cells and can arise during cell division or due to environmental factors. 

A virus or UV exposure are two things that can cause acquired mutations.

What Do Chromosomes Do?

Chromosomes carry hereditary information. This information determines many things about you, including how you look and how your body will react to its environment. Chromosomes are constructed of protein and one single molecule of DNA.

The information contained within your 46 chromosomes - approximately 24,000 genes – is what makes you different from all other people on earth.

Do All Humans Have 23 Pairs of Chromosomes?

No. Most do, but some changes occur for some people that result in issues with growth, development, and the body.

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

A change in the normal number of chromosomes, either a gain or loss, is called aneuploidy.  

The most common type of aneuploidy is trisomy. People with trisomy have an extra copy of one particular chromosome in each cell. For example, when the extra chromosome copied is chromosome 21, the person is diagnosed with trisomy 21, better known as Down syndrome.

When the opposite occurs – a person has one less chromosome – it is monosomy. In this case, one particular chromosome was copied only once instead of twice. One of the most common types of monosomy is Turner syndrome. This syndrome affects women and causes them to have just one copy of the X chromosome.

In some cases, a person might have a complete extra set of chromosomes or two additional sets of chromosomes. There are also cases in which an individual has two or more cell populations with different makeup. This is chromosomal mosaicism.

Chromosomal mosaicism is a condition that is caused by an error in cell division. Some cells end up with one additional or one missing chromosome, which means there might be 45 or 47 chromosomes in a cell. Another type of Turner syndrome, Mosaic Turner syndrome, is an example of chromosomal mosaicism.

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

Cell Mutation and Cancer

Many types of cancer occur because of changes in the number of chromosomes in cells. They are not inherited changes. Instead, they occur in non-egg or non-sperm cells that are called somatic cells. The changes 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, the risk is higher for cancer when you have inherited an abnormal copy of a gene. This means cells start with one mutation, so it’s easier and quicker for enough mutations to build up and develop into cancer.

But you don’t need to be born with “cancer-prone” genes to develop cancer. Gene mutations occur throughout your life, and in most cases, these acquired mutations cause cancer. 

The most common causes of acquired gene mutations are cigarette smoking, radiation, diet, and hormones. It’s also possible for mutations to occur randomly when human cells divide.

Most of the time, your body’s cells detect unusual changes and repair them. When repair doesn’t occur, the cell will die in a process called apoptosis.

But when either of the things does not occur, and a cell survives an unusual change, it may lead to a person developing cancer.


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Resources

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“National Human Genome Research Institute Home | NHGRI.” Www.Genome.Gov, genome.gov.

Genetics Home Reference. “Genetics Home Reference, Your Guide to Understanding Genetic Conditions.” Genetics Home Reference, 2019, ghr.nlm.nih.gov.

“Can Changes in the Number of Chromosomes Affect Health and Development?: MedlinePlus Genetics.” Medlineplus.Gov, medlineplus.gov/genetics/understanding/mutationsanddisorders/chromosomalconditions/. Accessed 30 Sept. 2020.

Cancer.Org, American Cancer Society, 2014, www.cancer.org/cancer/cancer-causes/genetics/genes-and-cancer/gene-changes.html.

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