23 Chromosomes And Their Functions

Edited By Irshad Anwar | Updated on Jul 21, 2025 03:55 PM IST

The cell has a nucleus, in which the DNA molecule is present. The DNA is packaged into thread-like structures called the chromosomes. Each chromosome is made of DNA tightly coiled around histone proteins, which help support its structure.

Chromosomes are not directly visible in the cell’s nucleus, nor under the microscope as well. However, the DNA which helps make up the chromosome becomes more tightly packed during cell division. Then, it can be visible under the microscope. Researchers study the chromosomes only when the cell is undergoing cell division. 23 chromosomes and their function is a topic of the chapter Principles of Inheritance and Variation in Biology.

NEET 2025: Mock Test Series | Syllabus | High Scoring Topics | PYQs

NEET Important PYQ's Subject wise: Physics | Chemistry | Biology

New: Meet Careers360 B.Tech/NEET Experts in your City | Book your Seat now

This Story also Contains

What are Chromosomes?
Types of Chromosomes
23 Chromosomes and their Functions
How Many Chromosomes Do Down Syndrome Have?
MCQs on Genetics

23 Chromosomes And Their Functions

What are Chromosomes?

Humans have 23 chromosomes and their functions include determining physical traits like height and eye color. The 23 chromosomes' names are designated by numbers from 1 to 22, with the last pair being X and Y. Understanding how many chromosomes a female has can provide insights into sex-linked genetic conditions. The term 23 chromosomes refers to the total number of chromosomes found in human somatic cells.

Types of Chromosomes

The chromosomes are divided into autosomal chromosomes and sex chromosomes. Autosomes are mainly present in the somatic cell of the body, whereas sex chromosomes are present in the reproductive cells of the body.

A. Autosomes and Sex Chromosomes(Allosomes)

Human chromosomes are the majority of two different types namely - autosomes and allosomes.
Genetic traits that are usually associated with the sex of the person are transferred on through the sex chromosomes. The left genetic information is associated with the autosomes.
Humans possess 23 pairs of chromosomes in their cells, out of which 22 pairs are termed to be as autosomes and one pair is termed to be as sex chromosomes, making a total of 46 chromosomes in each cell.
Understanding how many chromosomes do humans have is fundamental for studying human genetics and evolution.

B. On the Basis of Number of Centromeres

Monocentric: These are chromosomes with one centromere.
Dicentric: These are chromosomes with two centromeres.
Polycentric:These are chromosomes with more than two centromeres
Acentric: These are chromosomes without the involvement of centromere. This type of chromosome shows freshly broken segments of chromosomes which do not live for long.
Diffused or non-located: These are chromosomes with indistinct centromeres that are usually diffused throughout the whole length of the chromosome.

NEET Highest Scoring Chapters & Topics

Know Most Scoring Concepts in NEET 2024 Based on Previous Year Analysis.

Know More

23 Chromosomes and their Functions

Humans possess a total of 23 chromosomes in humans, arranged into pairs that carry genetic information. Here's a summary table on the functions and disorders associated with each chromosome that you learned in this lesson:

Chromosome	Description
Chromosome 1	Chromosome 1 contains 2,000 to 2,100 genes responsible for instructions for making proteins. It is the largest chromosome present in the human body among the total 23 pairs of chromosomes.
Chromosome 2	It is found to be the second largest human chromosome and is responsible for the longest known protein-coding sequence, a 280,000 base pair gene for a muscle protein called titin.
Chromosome 3	This chromosome includes gene clusters responsible for coding olfactory receptors (involved in the sense of smell) and chemokine receptors that aid inflammatory processes.
Chromosome 4	Chromosome 4 codes for genes related to Huntington's disease and polycystic kidney disease, as well as muscular dystrophy and various inherited disorders.
Chromosome 5	This chromosome plays a major role in cell growth and cell division.
Chromosome 6	Chromosome 6 is associated with over 120 genes for major human diseases, including cancer, heart disease, and some infectious and inflammatory disorders.
Chromosome 7	Its deletion causes Williams syndrome and is involved in body growth.
Chromosome 8	This chromosome is responsible for normal brain formation and developmental variations, including small head size or facial differences.
Chromosome 9	Responsible for body growth and division; it contains a gene for hexokinase.
Chromosome 10	Contains 700-800 genes responsible for making proteins, including the gene for the ABO blood group.
Chromosome 11	Contains genes for insulin and catalase; its deficiency leads to Ataxia telangiectasia.
Chromosome 12	Contains genes for Collagen II and alpha-1 salivary protein complex; its deficiency leads to Phenylketonuria and Pallister-Killian syndrome.
Chromosome 13	Contains genes for Collagen IV alpha-1 chain and alpha-2 chain ribosomal RNA; its deficiency leads to Patau syndrome, retinoblastoma, and Wilson’s disease.
Chromosome 14	Contains genes for T-cell leukemia-1 and immunoglobulin heavy chain gene cluster ribosomal RNA; its deficiency leads to Alzheimer's, Burkitt’s lymphoma, and multiple myeloma.
Chromosome 15	Contains genes for ribosomal RNA; its deficiency leads to Tay-Sachs disease, Marfan syndrome, and Prader-Willi syndrome.
Chromosome 17	Contains growth hormone; its abnormalities can cause Charcot-Marie-Tooth disease.
Chromosome 18	Has genes related to gastric releasing peptide; its deficiency can cause Niemann-Pick disease.
Chromosome 19	Contains genes related to the Bombay phenotype (green/blue eye color); its deficiency can cause myotonic dystrophy or maple syrup urine disease.
Chromosome 20	Responsible for growth hormone-releasing factor (somatocrinin); dysfunction can lead to Alagille syndrome.
Chromosome 21	Contains ribosomal RNA; associated with genetic disorders like Down syndrome and autoimmune polyendocrine syndrome.
Chromosome 22	Responsible for several important genes related to immune system function; it also plays a role in neurological development and disorders.
Chromosome XX	Contains genes for Haemophilia A (factor VIII) and Haemophilia B (factor IX); can cause disorders like Turner syndrome and Haemophilia A.
Chromosome XY	Contains genes related to pseudoautosomal segments, testicular determining factor, azoospermia-third factor, and H-Y antigen; abnormalities can lead to genetic diseases like Y chromosome microdeletion or XYY syndrome.

How Many Chromosomes Do Down Syndrome Have?

People with Down syndrome have an extra chromosome; therefore, how many chromosomes do they have? The answer is 47.
The number of chromosomes in the case of Down syndrome is necessary to understand for early diagnosis and subsequently, intervention strategies.
Trisomy 21 is the number of chromosomes found in Down syndrome; it consequently explains how many chromosomes lead to various developmental challenges.
As a matter of fact, testing with genetics often tells how many chromosomes Down syndrome has and this helps to confirm the diagnosis.
The number of chromosomes, which the children suffer from in Down syndrome helps the medical professionals provide appropriate care and support.

Understanding the 23 chromosomes and their functions is crucial for identifying genetic disorders that can arise from mutations.The 23 chromosome names help in diagnosing genetic conditions by identifying which chromosome is affected.Knowing how many chromosomes do humans have plays a crucial role in identifying chromosomal abnormalities during medical assessments.

MCQs on Genetics

Q1. Assertion: Genetic information is passed from parent to offspring.

Reason: Offspring inherit half of their genetic information from each of their parents during sexual reproduction.

Option 1: Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Option 2: Both Assertion and Reason are accurate, but Reason does not adequately explain Assertion.

Option 3: The assertion is correct, but the reasoning is incorrect.

Option 4: Both Assertion and Reason are incorrect.

Correct answer: 1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Explanation:

In sexual reproduction, the genetic information of two parents is combined to create a unique offspring. Each parent contributes half of their genetic material to the offspring, which determines the physical and biological characteristics of the offspring. The genetic material is carried in the form of DNA, which contains the genetic code that determines traits such as eye colour, height, and susceptibility to certain diseases.

Hence, the correct answer is Option (1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Q2. Assertion: Genetic mutations can lead to changes in the traits of an organism.

Reason: Mutations can alter the DNA sequence, which can affect the expression of genes and lead to changes in physical or biological traits.

Option 1: Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Option 2: Both Assertion and Reason are accurate, but Reason does not adequately explain Assertion.

Option 3: The assertion is correct, but the reasoning is incorrect.

Option 4: Both Assertion and Reason are incorrect.

Correct answer: (1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Explanation:

Genetic mutations can develop naturally or as a consequence of exposure to certain chemicals or radiation in the environment. These mutations can change the DNA sequence, which can impact how genes are expressed and eventually result in modifications to a person's biological or physical characteristics. While some mutations may have little to no impact on the organism, others may have a major one, such as the development of diseases or changes to the organism's appearance. In areas like medicine and agriculture, where researchers can use this knowledge to breed crops with desirable characteristics or develop treatments for genetic diseases, understanding genetic mutations is crucial.

Hence, the correct answer is Option (1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Q3. Which of the following is the basic unit of heredity in living organisms?

Option 1: Genotype

Option 2: Phenotype

Option 3: Chromosome

Option 4: Gene

Correct answer: 4) Gene

Explanation:

A gene is the basic unit of heredity. It is a segment of DNA that contains instructions for the production of a specific protein or functional RNA molecule. Genes are responsible for the traits and characteristics that are passed down from parents to offspring.

Hence, the correct answer is Option 4) Gene

Also Read:

Frequently Asked Questions (FAQs)

1. What is the function of chromosome 16?

It contains genes for Nonhistone chromosomal protein 1 and also for Hemoglobin alpha and Haemoglobin zeta. Its deficiency leads to Familial Mediterranean fever and Thalassemia.

2. What is the function of sex chromosomes?

Sex chromosomes play a great role in the determination of sex of the child. If the X chromosome comes from the male and X chromosome comes from the female then it will be a female child and if X comes from female and Y chromosome comes from the male then it will be a male child.

3. What is genetic mapping?

Geneticists make the use of 'map unit’ to calculate the distance between linked genes. It is defined as a diagrammatic graphical representation that shows the exact arrangement, and combination of genes in a linkage group of chromosomes.

4. What is meant by karyotype and idiogram?

Karyotype is defined as the entire set of chromosomes of a cell or individual, as represented during mitotic metaphase.Idiogram is defined as the diagrammatic representation of a karyotype. in an ideogram, the chromosomes of a haploid set of an organism are numbered in a series of decreasing sizes

5. How does chromosome 21 relate to Down syndrome?

Down syndrome occurs when there's an extra copy of chromosome 21 (trisomy 21). This chromosome is one of the smallest but contains genes crucial for brain development. The extra genetic material leads to the characteristic features of Down syndrome.