Gayathri Mani

Human Chromosomes Study Guide

Human Chromosomes are condensed DNA strands wrapped around a protein called histones. They are responsible for passing the genetic information to the offspring.


Charles Darwin, while studying the evolution of species in the 19th century, observed that for a species to survive, adaptation and reproduction are crucial. Therefore, it is important to develop qualities that align with the changing environment and resource needs.

Hence, over the years, our physical structure has started deviating from that of our ancestors. This happens because survival traits are passed on from the parents to their offspring. This is conducive for untethered reproduction, which leads to a healthy population.

DNA and Chromosomes

However, Darwin could not explain the mechanism responsible for passing on the traits. In 1921, chromosomes in humans were discovered in cancer cells and were counted conclusively. Chromosomes can be observed under light microscopes, which led to many advanced studies in the field.

The human genome Source

What is a chromosome?

The word chromosome is derived from the Greek words "chroma" and "soma." Chroma means color, and soma means body. Therefore, scientists recognize this cell structure as a colored body. The reason behind this nomenclature is that chromosomes stain when subjected to colored dyes during research. To simplify the idea, human chromosomes are nothing but DNA strands wrapped around proteins called histones. Now, DNA strands can be quite long to fit inside the plant or animal nucleus. Therefore, histones provide a condensed form to the DNA strand to fit within the nucleus. Each chromosome is divided into two parts by centromere.

DNA stands for Deoxyribonucleic Acid, which carries unique traits. Thus, we can conclude that chromosomes carry crucial genetic information. Now, the question here is that how many human chromosomes are there? Every human has a total of 23 pairs of chromosomes.

We inherit 23 chromosomes from each parent, which accounts for our uncanny resemblance in physical structure and behavior. Additionally, the chromosome number must remain intact for a healthy life.

In some of the cancer patients, fragmented chromosome pairs have been observed. Similarly, patients with Down Syndrome carry 47 chromosomes because they have a replica of the 21st chromosome. Let's dive further into this article to find more about chromosomes and what they do.

Human chromosomes Source

What do chromosomes do?

The function of the chromosomes is to protect the DNA's structure. As discussed earlier, chromosomes have a protein called histones that condenses the DNA, which allows it to fit inside the nuclei. If not for the chromosomes, DNA would float around our body unwounded.

If we connect all the DNA strands in our body, the resulting structure would be as long as 6ft. Now, we know that one of the basic biological principles for human survival is that new ones must replace the old cells during mitosis.

This is the part where cell division occurs. It is the responsibility of the chromosomes to keep the DNA intact during cell division so that exact copies are made. When faults occur in DNA replication, it leads to serious health issues.

For example, patients with Leukemia have damaged pieces of chromosomes joined together. Similarly, it is also crucial that the egg cells and sperm cells have the exact number of chromosomes, and these chromosomes must be in perfect shape. Otherwise, the offspring might suffer from chronic diseases like Down syndrome.

Do all living things have the same type of chromosomes?

This is a recurring question for most of us. Since most living beings survive in accordance with basic biological principles, it only makes sense that they have the same type of chromosomes.

Now, this is true for the most part, but in the case of much smaller beings like bacteria, they have a single pair of circular chromosomes. Complex beings like humans carry linear chromosomes in each cell (except the reproductive cells - those are called gametes)

Gametes carry only one part of each pair of chromosomes. When two reproductive cells unite, one cell with a pair of chromosomes is formed. Due to perpetual mitosis or cell division, copies of these chromosomes are made, and the offspring with unique traits are born.

Moreover, we have one other type of chromosome found within the mitochondria. These chromosomes resemble those found in bacterias and are located outside the nucleus. The function of these chromosomes is to act as a powerhouse of the cell.

What are centromeres?

Looking at the chromosomes under a microscope, you will observe a constricted region. This constricted region is called the centromere. Although it is named centromere, it may not always be found in the center of the chromosome structure. Sometimes, you may find the centromere on one end of the chromosome.

centromere Source

The regions on each end of the centromere are known as chromosome arms. The function of the centromere is to keep the chromosomes intact during the cell division process. During cell division, the centromere is the attachment site for two halves of the replicated chromosomes.


  • If we look at the question in which year chromosomes were discovered? The answer should be 1921.
  • Chromosomes are DNA strands wrapped around proteins called histones.
  • Chromosomes are present inside the plant and animal nucleus.
  • Chromosomes facilitate the proper replication of DNA during cell division.
  • Humans have a total of 23 pairs or 46 chromosomes in total.
  • The sex chromosome in females is XX, while in males, it is XY.


1. What is the 23 chromosome in humans?

Humans have 23 pairs of chromosomes, which is 46 numbers of chromosomes in total. We inherit 23 chromosomes from each of our parents.

2. Why do humans have 23 sets of chromosomes?

Human chromosomes exist in matching pairs. Therefore, humans are categorized in one of those labeled as diploids. We inherit 23 chromosomes from each of our parents. Therefore, our haploid number is 23, and the diploid number is 46.

3. Do humans have 32 chromosomes?

No. Humans have a total of 46 chromosomes in human cells or 23 pairs of chromosomes. However, the human genome has 32 chromosomes, which are used for DNA fingerprinting.

4. Do humans have 24 chromosomes?

No. Humans have an exact number of 46 chromosomes. Any distortion in this number may lead to serious health issues.


  1. Human Chromosomes. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/3.9/primary/lesson/human-chromosomes-and-genes-bio/ Accessed 13 Dec, 2021.
  2. Chromosome. https://www.genome.gov/genetics-glossary/Chromosome Accessed 13 Dec, 2021.