DNA, Genes & Chromosomes


What is DNA?

Deoxyribonucleic acid (DNA) is the material that exists in every cell in your body that holds your genetic code. It makes up your body’s instruction manual.

What is DNA made of?

DNA has a language that it uses to write your instruction manual (a code). Four chemical bases make up your DNA language including:

  • Adenine (A).
  • Cytosine (C).
  • Thymine (T).
  • Guanine (G).

These four bases arrange themselves in order to form “words” in your instruction manual.

DNA constantly replicates itself by making hand-written copies of your body’s instruction manual using the chunks of bases that form the words. There are an estimated 3 billion bases in a human’s body. About 99% of those bases are the same in every person. The remaining 1% is what makes you unique.

What are genes?

Genes are the building blocks for your body. Some genes give the instructions to make proteins. A protein’s job is to tell your body what types of physical characteristics you should have, like your hair and eye color. Some genes code for RNA, which does other jobs.

How do I get genes?

You can’t buy genes from a department store. You inherit your genes from your parents. You receive one copy of a gene from each parent (one from the egg and one from the sperm). Once you receive a pair, your genes divide and copy themselves until your body has enough genes to fill your instruction manual. There are approximately 20,000 to 25,000 genes in your body.

What are chromosomes?

Chromosomes are structures that look like thread, which live in the nucleus (center) of cells. One molecule of DNA and one protein make up one chromosome. Chromosomes are different sizes, and proteins called histones allow them to pack up small enough to fit in a nucleus. Without these, our chromosomes would be as tall as we are! Chromosomes give your cells the actual instructions to make you into a unique person.

How many chromosomes do humans have?

Humans should have 23 pairs of chromosomes (46 total). Chromosomes divide into 22 numbered pairs (autosomes) and one pair of sex chromosomes (X and Y). You receive one chromosome from each parent to make a pair.

Although rare, errors occur when cells divide and replicate, so people might have an additional chromosome attached to a pair (trisomy) or one less chromosome on a pair (monosomy).


What is the relationship and function of DNA, genes and chromosomes?

DNA, genes and chromosomes work together to make you who you are. Chromosomes carry DNA in cells. DNA is responsible for building and maintaining your human structure. Genes are segments of your DNA, which give you physical characteristics that make you unique. Together, your body has a complete instruction manual that tells your cells how to behave.


Where is DNA located?

DNA can be found in each cell in your body. The majority of your DNA resides in the nucleus (center) of each cell in your body and some DNA lives in mitochondria (little organelles inside of your cells that produce energy).

What does DNA look like?

Your DNA structure is made up of four base pairs: adenine (A), cytosine (C), thymine (T), and guanine (G). The bases form pairs (base pairs); A with T and C with G. The base pairs connect with a sugar molecule and a phosphate molecule (making a nucleotide) that form a spiral staircase (double helix). The base pairs are the steps and the sugar and phosphate molecules are the handrails.

What do chromosomes look like?

Chromosomes have a structure that is like a thread. Chromosome proteins (histones) wrap up DNA like a spool to make it small enough to fit into your cells. If chromosomes didn’t wrap around DNA, your DNA would be 6 feet long from end to end.

Conditions and Disorders

What are genetic conditions?

A genetic condition is a disease caused by a gene that isn’t normal. A genetic mutation is a gene that didn’t copy correctly during cell division, and it has a different sequence or shape from other genes in the body. When you have a genetic mutation, your body can’t develop normal form and function.

Sometimes you can inherit the genetic mutation from a parent and sometimes the gene mutates randomly mutates in you, with no history of the mutated gene or the genetic condition in your family.

There are thousands of genetic conditions that exist.

How do genetic mutations happen?

Genetic mutations occur during cell division when your cells divide and replicate. When your cells divide, they hand-write your body’s instruction manual by copying the original document word for word. During this process, there is a lot of room for error because your cells might skip a page or a chapter while rewriting. If you have an error (genetic mutations), your instruction manual gives your body the wrong directions. Sometimes a mutation doesn’t change how your body works,but sometimes that mutation means that you can’t function normally. It all depends on just what the gene codes for.

What tests check the health of my genes?

There are a variety of genetic tests that use a sample of your blood, skin, hair or a fetus’s amniotic fluid to identify changes to your genes, chromosomes or proteins in your body. Genetic testing can pinpoint specific genetic conditions and identify mutated genes. This test can also let you know if you are at risk of having a child with a genetic condition if you plan on becoming pregnant.


How do I improve the health of my DNA?

To improve the health of your DNA, take steps to take care of your body since your DNA is responsible for how you form and function. You can improve your overall health by:

  • Eating a well-balanced diet.
  • Exercising.
  • Maintaining a healthy weight.
  • Avoid smoking and using tobacco products.

Frequently Asked Questions

What is a homologous chromosome?

A homologous chromosome is made up of one chromosome from each parent, with the same genetic material in the same place on each chromosome. Chromosomes can be nonhomologous, meaning that they have genetic material that is different or in a different place on each chromosome.

A note from Cleveland Clinic

Your DNA, genes and chromosomes are essential components of your body that make you who you are. Although these components are extremely microscopic, they have a remarkable duty. Keep your DNA, genes and chromosomes in working order by living a healthy lifestyle.

Last reviewed by a Cleveland Clinic medical professional on 05/20/2022.


  • National Human Genome Research Institute. Several pages reviewed for this article. (https://www.genome.gov/genetics-glossary/Deoxyribonucleic-Acid) Accessed 5/20/2022.
  • U.S. National Library of Medicine. Several pages reviewed for this article. (https://medlineplus.gov/genetics/understanding/basics/dna/) Accessed 5/20/2022.
  • YourGenome. Several pages reviewed for this article. (https://www.yourgenome.org/facts/what-is-dna) Accessed 5/20/2022.

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