What Are Chromosomes Made Of?

03/11/2022 | 4 min. read

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Our bodies are extremely complex. It involves an intricate network of tissues, nerve endings, organs, bones, muscles, and the list could go on.

At the micro level, the human body is composed of billions and billions of cells, only visible to the strongest microscopes. These cells house thread-like strands called chromosomes.

Many people are familiar with the word, but are unsure what chromosomes actually are.

What are they made of? And why are they so important? Let’s find out.

What Are Chromosomes?

Chromosomes were first discovered in the late 1800s, although the exact function of these cellular structures were unclear at first. In the early 1900s more research was done to better understand the exact nature of chromosomes and their role in heredity.

Even if it’s been many years since you’ve sat in a biology class, most can remember enough to know how important chromosomes are, especially in terms of genetics.

Chromosomes are thread-like structures that are located inside the nucleus of nearly every plant, animal, and human cell. The nucleus is the main control center of the cell, responsible for cellular activities.

The word chromosome is actually taken from Greek terms, chroma meaning color and soma meaning body. The emphasis on color is because these cell structures are heavily stained with dyes during research.

What Makes a Chromosome?

In short, chromosomes are made up of proteins and deoxyribonucleic acid (DNA).

DNA contains genetic information that directs how an organism develops and functions, and these instructions are passed from parent to offspring.

Spool-like proteins within the chromosomes, called histones, help keep DNA tightly wrapped. Molecules called nucleotides make up DNA.

These molecules contain a nitrogen base with a phosphate group and sugar group. The nitrogen base is composed of four types: Adenine, thymine, guanine, and cytosine.

These nucleotides attach together to form the famous double-helix structure of the DNA strand (i.e., the two spiraled long strands). The nitrogen bases on one strand pair with the bases on the other.

Human DNA, sometimes called the human genome, comprises over 3 billion base pairs. Interestingly, these pairs are nearly the same — 99 percent — in all people.

So, in short, chromosomes are the storehouse for your genetics.

Centromeres and Telomeres

Structurally, chromosomes have a constricted region that separates their long arms (q) from their short arms (p). This is known as a centromere. It is an important element after cellular division as it joins the chromatids together after DNA replication.

Telomeres refer to the tail ends of the linear chromosomes. These structures help protect the ends of the chromosomes. In effect, telomeres help keep the chromosomes from unraveling — sort of like the tip of a shoelace.

Researchers have discovered that telomeres shorten each time the cell divides. This has led many to believe that there is a correlation between telomere length and the aging process. Telomeres could be a reliable marker of biological age.

Chromosomes Role in Genetics

Cells must constantly divide to produce new cells to function and grow. These replace the old, worn-out cells. Chromosomes play a key role during this cellular division. They ensure the DNA remains intact and accurately copied, and evenly distributed among the cells during the process.

Problems can occur when chromosomes within the new cells arise, such as in the structure or the number. Defective chromosomes in new cells are responsible for some serious conditions, such as some types of cancers.

The biggest role that chromosomes play is in the area of genetics.

Genes, or heredity information, are made up of DNA and are contained within the chromosomes. Each chromosome contains hundreds to thousands of genes – totaling roughly 35,000.

But, genes aren’t unique to humans only; all living things contain genes, though the number of chromosome pairs does differ.

Chromosomes and Inherited Traits

Genes play an integral role in making you who you are — especially related to physical traits and how you look. These traits are passed down by or inherited through your parents.

There are two important terms to be aware of when speaking of genetics:

  • Genotype – Also called the genome, this refers to a person’s unique combination of genetic makeup. A genotype is essentially a set of instructions that tell the body to be built and function — gene expression.
  • Phenotype – This refers to the actual structure of a person’s body and its function. These are the observable traits — blood type, height, hair, and eye color.

In terms of genetics, a trait refers to any gene-determined characteristic, like eye or hair color. Human beings have 23 pairs of chromosomes, totaling 46, and these pairs are inherited from each parent.

Reproductive cells are the only cells in the human body that do not contain pairs of chromosomes; they only carry one copy of each. However, when two reproductive cells unite, they form a single cell that contains two copies from each chromosome.

A copy of each chromosome is inherited from the female parent and the male parent. One of the 23 pairs is sex chromosomes. Females have two X chromosomes while males have one X and one Y chromosome.

The other 22 chromosomes are called autosomes or non-sex chromosomes and are the same for females and males.


Our bodies are extremely complex organisms. They contain intricate cell structures known as chromosomes.

Made up of various protein structures, these chromosomes house important DNA strands, which contain our genetic information. This information is passed down or inherited from our parents.

While chromosomes are certainly complex and not definitively understood even today, we do know that they help make us who we are.


Genetics, Chromosomes - StatPearls NIH

Nucleus Play Audio |

Introduction - Mapping and Sequencing the Human Genome | NIH

Gene Expression | NIH

Healthy Directions Staff Editor