Understand in 3 Minutes! The Differences Between DNA, Genes, and Chromosomes

Last revised: July 4, 2025

An easy-to-understand explanation of the differences between DNA (deoxyribonucleic acid), genes, and chromosomes. DNA is the molecule that stores genetic information, genes are specific segments of DNA that serve as the body's blueprint, and chromosomes are the condensed structures formed by DNA. This article summarizes the basic knowledge helpful for understanding prenatal testing and DNA testing.

DNA (deoxyribonucleic acid), genes, and chromosomes are essential elements for understanding the genetic information of life. Each plays a different role while being closely related to the others. The human body is made up of a basic unit called the "cell." Inside the nucleus of this cell are "chromosomes," and part of the "DNA" within these chromosomes functions as "genes." As you hear the terms "DNA," "genes," and "chromosomes" more often in daily life, surprisingly few people can accurately explain what each one means and how they differ. Here, we clearly explain the definitions, roles, and relationships of DNA, genes, and chromosomes—terms that sound familiar but are often not well understood. We hope this helps you gain a proper understanding of prenatal testing and paternity/family testing.

What is DNA

DNA stands for "Deoxyribonucleic Acid" and is a substance found in nearly all living organisms that stores genetic information and passes it on to the next generation [ref:1]. DNA exists within the nucleus of cells and has a distinctive shape known as the double helix structure. This double helix structure was discovered in 1953 by James Watson and Francis Crick, and it is considered one of the most important discoveries in the history of biology [ref:3].

DNA is composed of four types of bases: adenine (A), thymine (T), cytosine (C), and guanine (G), and the sequence of these bases determines genetic information. Bases always form specific pairs, with adenine bonding to thymine and cytosine bonding to guanine. This mechanism of "complementary base pairing" allows DNA to be accurately replicated, ensuring that genetic information is faithfully copied each time a cell divides.

Human DNA is composed of approximately 3 billion base pairs, all contained within the nucleus of every cell. If you were to unwind and stretch out all the DNA contained in a single cell, it would measure about 2 meters in length, but in reality it is very intricately folded and compactly stored within a nucleus just a few micrometers in size [ref:2].

Main functions of DNA

• Storing genetic information: Records all information related to an organism's traits and characteristics
• Self-replication: Accurately copied during cell division and passes information to new cells
• Instructing protein synthesis: Provides the design information for the proteins that make up the body, via mRNA (messenger RNA)
• Passing genetic information across generations: Transmits genetic information from parent to child, generation after generation

What is a gene

A gene is a specific sequence segment of DNA that contains the information determining an organism's traits and characteristics (such as eye color, hair color, blood type, alcohol tolerance, and whether the eyelid is single or double). Genes function as the "blueprint" that builds the human body, and humans have approximately 20,000 to 25,000 genes [ref:2].

Because genes are passed down from parent to child across generations, similar traits and characteristics are often seen among family members. For example, having the same eye color as your father or a similar constitution to your mother is the result of inherited genes.

However, the portion of the entire DNA that actually functions as genes is only about 1.5 to 2%. The remaining more than 98% is called "non-coding region," which used to be referred to as "junk DNA," but recent research has revealed that it plays important roles such as regulating gene expression [ref:4].

Representative traits determined by genes

Genes are involved in many of our body's characteristics. Below are some representative examples.

As shown here, a single trait is usually not determined by just one gene; rather, multiple genes interact in complex ways to determine a trait. Environmental factors are also added into the mix, ultimately determining the final phenotype (the characteristics that actually appear).

What is a chromosome

A chromosome exists within the nucleus of a cell and is formed when about 2 meters of DNA wraps around proteins called histones, becoming compactly condensed. Human somatic cells have 46 chromosomes (23 pairs), of which 22 pairs are autosomes and 1 pair is sex chromosomes (XX or XY) [ref:1].

Chromosomes are accurately replicated and passed on to new cells during the process of cell division (the process by which organisms increase their cells in order to grow). If an error in genetic information occurs during this process, it can cause hereditary diseases. For example, abnormalities in the number or structure of chromosomes can result in hereditary conditions such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Turner syndrome (monosomy X).

Difference between autosomes and sex chromosomes

The 23 pairs of chromosomes can be broadly divided into two types.

• Autosomes (22 pairs, 44 chromosomes): Chromosomes common to both sexes, containing genes that determine various physical characteristics of the body
• Sex chromosomes (1 pair, 2 chromosomes): Chromosomes that determine biological sex. Females have an XX combination, and males have an XY combination

A child inherits 23 chromosomes each from the father and mother, for a total of 46 chromosomes. Regarding the sex chromosomes among these, the child always receives an X chromosome from the mother, while receiving either an X or Y chromosome from the father, and it is this combination that determines the child's biological sex.

Chromosomal abnormalities and disease

Abnormalities in the number or structure of chromosomes can lead to various diseases. Representative examples include the following.

1. Numerical abnormalities: When the number of chromosomes is greater (trisomy) or fewer (monosomy) than normal. Down syndrome (an extra copy of chromosome 21) is a representative example
2. Structural abnormalities: Changes in structure such as deletion, translocation, inversion, or duplication of part of a chromosome. This includes conditions such as 5p deletion syndrome (cri-du-chat syndrome)
3. Sex chromosome abnormalities: Abnormalities in the number of sex chromosomes. Examples include Turner syndrome (only one X chromosome) and Klinefelter syndrome (XXY)

The relationship between DNA, genes, and chromosomes

DNA, genes, and chromosomes are each independent concepts, yet they exist in a hierarchical relationship. To make this relationship easier to understand, let's compare human genetic information to a town [ref:5].

• Chromosomes correspond to the 46 buildings that make up the town
• Genes correspond to the rooms that exist within those buildings
• DNA is like the individual blocks that make up each building

In other words, DNA (the blocks) comes together to form genes (the rooms), and the entire DNA containing the genes is condensed together with proteins to become a chromosome (the building)—this is the hierarchical structure at play.

To organize this a bit more scientifically: DNA is the "material" itself that records genetic information, genes are "meaningful units of information" within the DNA, and chromosomes are the "physical package of information" formed by DNA together with its associated proteins. It is through the coordinated function of these three elements that our bodies are accurately formed and maintained.

Connection to prenatal testing and DNA testing

Understanding DNA, genes, and chromosomes is extremely important for correctly understanding prenatal testing and parent-child DNA testing.

Connection to Non-Invasive Prenatal Testing (NIPT)

NIPT (Non-Invasive Prenatal Testing) is a screening test that analyzes fetal-derived DNA fragments (cell-free DNA) contained in a pregnant woman's blood to check for chromosomal abnormalities in the fetus. Specifically, it can check for numerical chromosomal abnormalities such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Because the test can be performed simply by drawing the mother's blood, it is widely used as a non-invasive testing method that poses extremely low risk to the fetus.

Connection to parent-child DNA testing

Parent-child DNA testing analyzes specific regions of DNA (STR: short tandem repeats) to confirm the biological blood relationship between parent and child. Because a child inherits half of their DNA from each parent, comparing the child's DNA pattern with the DNA pattern of the presumed parent allows the parent-child relationship to be determined with high accuracy. Testing during pregnancy (prenatal paternity testing) is also possible, using fetal DNA present in the mother's blood.

Summary

DNA is the molecule that stores genetic information, and genes are specific portions of that DNA that determine an organism's traits and characteristics. Chromosomes are structures in which DNA is compactly condensed, playing the role of accurately transmitting genetic information during cell division.

These three elements play an essential role in the maintenance and evolution of life, and are deeply involved in the growth of organisms and the transmission of genetic information. Understanding this basic knowledge is the first step toward correctly making use of modern genetic medical services such as prenatal testing and DNA testing. We hope that having accurate knowledge about genetic information will help you make better decisions regarding your own health and that of your family.

／ Find out who the father of your baby is during pregnancy ＼

Learn more about prenatal parent-child DNA testing here

／ Check your baby's hereditary disease risk during pregnancy ＼

Learn more about Non-Invasive Prenatal Testing (NIPT) here

Frequently Asked Questions

Q1. What is the difference between DNA and genes?

A. DNA refers to the substance (molecule) itself that stores genetic information. A gene, on the other hand, refers to a "meaningful segment of information" within the DNA that carries instructions for making a specific protein. In other words, a gene is a part of DNA, and approximately 20,000 to 25,000 genes are scattered throughout the long DNA molecule [ref:2].

Q2. What effects can an abnormal number of chromosomes have?

A. An abnormal number of chromosomes can result in hereditary conditions such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), and Turner syndrome (monosomy X). These can be screened for in advance through prenatal testing (such as NIPT).

Q3. How many chromosomes do humans have?

A. Human somatic cells have 46 chromosomes (23 pairs). Of these, 22 pairs (44 chromosomes) are autosomes, and 1 pair (2 chromosomes) are sex chromosomes. Sex chromosomes are XX in females and XY in males, and they play the role of determining the child's biological sex [ref:1].

Q4. Which of DNA, genes, or chromosomes does NIPT examine?

A. NIPT analyzes cell-free DNA of fetal origin contained in a pregnant woman's blood, mainly to check for numerical chromosomal abnormalities (such as trisomies). In other words, it is a test that uses DNA as the analytical means to detect abnormalities at the chromosome level.

Q5. Why can DNA testing determine a parent-child relationship?

A. A child inherits half of their DNA (23 chromosomes) from each of the father and mother. Therefore, by comparing the child's DNA pattern (STR: short tandem repeats) with the parent's DNA pattern, a biological parent-child relationship can be determined with an accuracy of 99.99% or higher.

Q6. What is the double helix structure of DNA?

A. The double helix structure of DNA refers to the shape formed when two strands of DNA wind around each other in a helical form. It was discovered in 1953 by Watson and Crick. The two strands are joined by complementary base pairing (A with T, C with G), and this structure enables the accurate replication of DNA [ref:3].

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