23 Chromosomes And Their Functions

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:22 PM IST

Chromosomes are significant structures in human genetics. There are 23 in each set, and in total, there are 46 chromosomes in humans. These consist of 22 pairs of autosomes, which are chromosomes individuals do not have sex-linked; therefore, males have XY and females have XX. Each chromosome has specific genes which help in the handling of diverse functions and traits. For instance, chromosome 22 carries genes involved in the immune response and neurological functions. Conditions that include an additional copy of chromosome 21 comprise Down syndrome. The Chapter "Principles of Inheritance and Variation" of Biology focuses precisely on this theme; very important for students appearing for entrance exams like NEET and JEE, who should know about the 23 chromosomes and their functions.

This Story also Contains

Types Of Chromosomes
How Many Chromosomes Do Down Syndrome Have?
Tips, Tricks, And Strategies To Prepare For 23 Chromosomes And Their Functions
Weightage Of 23 Chromosomes And Their Functions In Different Entrance Exams
Types Of Questions Asked On The Topic 23 Chromosomes And Their Functions In Different Exams

Types Of 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.

Also Read:

A. Autosomes And Sex Chromosomes(Allosomes)

Human chromosomes are the majority of two different types namely - autosomes and sex chromosomes.
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.

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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.

List Of 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 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.

Tips, Tricks, And Strategies To Prepare For 23 Chromosomes And Their Functions

Here’s a table summarizing Tips, Tricks, and Strategies to Prepare for 23 Chromosomes and Their Functions:

Tip/Strategy	Description
Mnemonic Devices	Create memorable phrases to recall the 23 chromosomes and their functions easily.
Visual Aids	Use endocrine system diagrams and labelled images to visualize chromosome structures.
Flashcards	Make flashcards for each chromosome, including its name, function, and associated disorders.
Group Study	Discuss the 23 chromosomes names and their functions with peers to enhance understanding.
Practice Questions	Solve previous years' exam questions related to the topic to familiarize yourself with formats.

Here’s a concise mnemonic table summarizing the key points from the article about chromosomes:

Key Concept	Mnemonic Phrase	Summary
Total Chromosomes	"46 Total, 23 Pairs"	Humans have 46 chromosomes arranged in 23 pairs: 22 autosomes and 1 pair of sex chromosomes (XX/XY).
Functions of Chromosomes	"Genes Determine Traits"	Chromosomes carry genes that determine traits like height and eye color, and play roles in various diseases.
Down Syndrome	"Extra 21"	Individuals with Down syndrome have an extra chromosome, totaling 47 chromosomes (Trisomy 21).
Chromosome 22	"Immune and Neurological"	Chromosome 22 is responsible for genes related to immune function and neurological development.
Chromosome Disorders	"Specific Deficiencies"	Each chromosome is linked to specific disorders, such as Huntington's disease (Chromosome 4) and Tay-Sachs disease (Chromosome 15).

Weightage Of 23 Chromosomes And Their Functions In Different Entrance Exams

The weightage of the topic 23 Chromosomes and Their Functions have been discussed below:

Entrance Exam	Weightage	Estimated Percentage
NEET	High	15-20%
JEE Main	Moderate	10-15%
JEE Advanced	Moderate	10-15%
AIIMS	High	15-20%
UPSC (Biology Section)	Moderate	10-15%

Types Of Questions Asked On The Topic 23 Chromosomes And Their Functions In Different Exams

The types of questions asked on 23 Chromosomes and Their Functions are discussed below:

Entrance Exam	Types of Questions
NEET	MCQs on functions and disorders
JEE Main	Conceptual questions on genetics
JEE Advanced	Application-based problems
AIIMS	Assertion-reason type questions
UPSC (Biology Section)	Descriptive questions on chromosome roles
State Medical Exams	Multiple-choice questions on disorders
CBSE Class 12 Biology	Short answer questions on definitions

Also Read:

Genetics Definition	Genetics
Gene Definition	Allele Definition
Mendelian Genetics	Mendel's Laws of Inheritance
Law Of Inheritance: Mendel's Contribution	Monohybrid Cross - Inheritance Of One Gene
What Are The Three Laws Of Inheritance?	Mendel's Law of Dominance

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.

6. What is aneuploidy and how does it affect an organism?

Aneuploidy is an abnormal number of chromosomes, either too many or too few. It can occur due to errors in cell division. The effects depend on which chromosomes are involved but often lead to developmental issues or genetic disorders, like Down syndrome (trisomy 21).

7. How do chromosomal abnormalities occur?

Chromosomal abnormalities can occur due to errors in cell division (meiosis or mitosis), exposure to certain environmental factors, or inherited from parents. These can involve changes in chromosome number (like trisomy) or structure (like translocations or deletions).

8. How do chromosomal deletions and duplications affect an organism?

Chromosomal deletions involve the loss of a chromosome segment, while duplications involve extra copies of a segment. Both can lead to genetic disorders by altering gene dosage. Deletions often cause more severe effects due to the loss of genetic information.

9. How do chromosomal abnormalities contribute to evolutionary processes?

Chromosomal abnormalities, while often detrimental, can sometimes lead to advantageous traits. Chromosomal rearrangements can create new gene combinations or alter gene expression patterns, potentially leading to new traits that might be favored by natural selection.

10. How do chromosomal inversions affect gene expression?

Chromosomal inversions occur when a segment of a chromosome is flipped 180 degrees. While they don't usually cause loss of genetic material, inversions can disrupt gene function if the breakpoints occur within genes or alter gene regulatory regions, potentially affecting gene expression.

11. What is the role of non-coding DNA on chromosomes?

Non-coding DNA, which doesn't directly code for proteins, plays various important roles. It includes regulatory sequences that control gene expression, structural elements like centromeres and telomeres, and sequences involved in chromosome packaging and organization.

12. What is the role of histone proteins in chromosome structure?

Histone proteins are crucial for packaging DNA into chromosomes. DNA wraps around histone octamers to form nucleosomes, the basic unit of chromatin. Modifications to histones can affect how tightly DNA is packaged, influencing gene accessibility and expression.

13. How do chromosomes contribute to species differentiation?

Chromosomes play a crucial role in species differentiation. Different species often have different numbers or structures of chromosomes, which can act as a reproductive barrier. Chromosomal rearrangements can also lead to the evolution of new species over time.

14. How do chromosomal abnormalities in gametes affect fertility and embryo development?

Chromosomal abnormalities in gametes can lead to infertility, miscarriage, or developmental disorders in offspring. Abnormalities might prevent proper fertilization or embryo implantation, or cause developmental issues if the embryo survives to term.

15. How do mitochondrial chromosomes differ from nuclear chromosomes?

Mitochondrial chromosomes are found in mitochondria, not the cell nucleus. They are circular, much smaller than nuclear chromosomes, and are typically inherited only from the mother. They contain genes essential for mitochondrial function and energy production.

16. How do homologous chromosomes differ from sister chromatids?

Homologous chromosomes are pairs of chromosomes that carry the same genes but may have different alleles. They come from different parents. Sister chromatids are identical copies of a single chromosome, created during DNA replication before cell division.

17. What is the centromere and its function on a chromosome?

The centromere is a constricted region on a chromosome that appears during cell division. It's where sister chromatids are joined and where spindle fibers attach during cell division to pull chromosomes apart. Its position helps classify chromosomes into different types.

18. What is the role of satellite DNA in chromosomes?

Satellite DNA consists of highly repetitive sequences often found near centromeres or telomeres. While its exact function is not fully understood, it's thought to play roles in chromosome structure, centromere function, and possibly in regulating nearby genes.

19. What is the significance of chromosome-specific repeat sequences?

Chromosome-specific repeat sequences are unique repetitive DNA sequences found on particular chromosomes. They play roles in chromosome structure and function, and are useful in identifying specific chromosomes or chromosome regions in genetic and forensic analyses.

20. How do the 23 chromosome pairs differ from each other?

Each chromosome pair differs in size, shape, and gene content. They are numbered 1-22 (from largest to smallest) plus the sex chromosomes (X and Y). Each pair carries different genes that control various traits and functions in the body.

21. What are sex chromosomes and how do they determine gender?

The 23rd pair of chromosomes are the sex chromosomes (X and Y). Typically, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome generally leads to male development.

22. Why is the Y chromosome unique among human chromosomes?

The Y chromosome is unique because it's much smaller than the X chromosome and contains fewer genes. It's passed only from father to son and carries genes crucial for male development, including the SRY gene that initiates male sex determination.

23. What are chromosomes and why do humans have 23 pairs?

Chromosomes are structures in cell nuclei that contain DNA and genes. Humans have 23 pairs (46 total) because we inherit one set of 23 from each parent, allowing for genetic diversity and the combination of traits from both parents.

24. What is the significance of chromosome 1?

Chromosome 1 is the largest human chromosome, containing about 8% of the total DNA in cells. It houses many important genes involved in neurological function, muscle contraction, and various genetic disorders.

25. What is a karyotype and how is it used?

A karyotype is a visual representation of a person's chromosomes, arranged in pairs by size and shape. It's used to detect chromosomal abnormalities, determine gender, and diagnose certain genetic disorders by revealing changes in chromosome number or structure.

26. What is the relationship between genes and chromosomes?

Genes are segments of DNA that code for specific proteins or traits, while chromosomes are structures that organize and carry these genes. Each chromosome contains many genes arranged in a specific order along its length.

27. What is the significance of chromosome banding patterns?

Chromosome banding patterns are distinctive stripes that appear when chromosomes are stained. These patterns are unique to each chromosome and help in identifying specific chromosomes, detecting structural abnormalities, and mapping genes to specific locations.

28. How do chromosomes contribute to genetic variation?

Chromosomes contribute to genetic variation through several mechanisms: independent assortment during meiosis, crossing over between homologous chromosomes, and random fertilization. These processes create unique combinations of genes in offspring.

29. What is the significance of the X-inactivation process in females?

X-inactivation is a process in female mammals where one of the two X chromosomes is randomly inactivated in each cell. This balances gene expression between males (XY) and females (XX), preventing females from having double the amount of X-linked gene products.

30. What is the role of telomeres on chromosomes?

Telomeres are protective structures at the ends of chromosomes. They prevent chromosomes from fusing or degrading during cell division. Telomeres shorten with each cell division, which is associated with aging and certain diseases.

31. How do chromosomes condense during cell division?

During cell division, chromosomes condense from long, thin strands into short, thick structures. This condensation is achieved through the coiling and supercoiling of DNA around proteins called histones, making the genetic material more compact and easier to separate.

32. How do chromosomes maintain their structure and integrity?

Chromosomes maintain their structure through several mechanisms: DNA is tightly wound around histone proteins, forming nucleosomes; special proteins help condense and organize the chromatin; and telomeres protect the chromosome ends from degradation.

33. What is genomic imprinting and how does it relate to chromosomes?

Genomic imprinting is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner. It involves chemical modifications to the DNA or associated proteins, affecting how genes on particular chromosomes are expressed without changing the DNA sequence.

34. What is the significance of chromosome territories in the cell nucleus?

Chromosome territories refer to the tendency of each chromosome to occupy a specific region in the nucleus. This organization is important for gene regulation, as it influences which genes are active or silent based on their position within the nucleus.

35. What is the relationship between chromosomes and cancer development?

Chromosomal abnormalities are common in cancer cells. These can include translocations, deletions, or duplications that activate oncogenes or inactivate tumor suppressor genes. Some specific chromosomal changes are associated with particular types of cancer.

36. What is the significance of chromosome painting techniques?

Chromosome painting is a cytogenetic technique that uses fluorescent probes to visualize specific chromosomes or chromosome regions. It's valuable for detecting chromosomal abnormalities, studying evolutionary relationships between species, and analyzing complex chromosomal rearrangements.

37. What is the role of the nucleolus in relation to chromosomes?

The nucleolus forms around specific regions of certain chromosomes called nucleolar organizer regions (NORs). These regions contain genes for ribosomal RNA. The nucleolus is where ribosomal RNA is transcribed and ribosomal subunits are assembled.

38. What is the relationship between chromosomes and epigenetic modifications?

Epigenetic modifications, such as DNA methylation and histone modifications, occur on chromosomes and affect gene expression without changing the DNA sequence. These modifications can be influenced by environmental factors and can sometimes be inherited.

39. What is the role of cohesin proteins in chromosome function?

Cohesin proteins play a crucial role in holding sister chromatids together after DNA replication. They're important for proper chromosome segregation during cell division and also play roles in DNA repair and gene regulation.

40. What is the significance of chromosome condensation factors?

Chromosome condensation factors are proteins that help compact chromosomes during cell division. They're crucial for proper chromosome segregation, as they ensure chromosomes are compact enough to be separated without tangling or breaking.

41. How do chromosomes contribute to cellular differentiation?

While all cells in an organism typically contain the same chromosomes, different genes are activated or silenced in different cell types. This differential gene expression, controlled by various factors including chromosome structure and epigenetic modifications, leads to cellular differentiation.

42. What is the role of lamins in chromosome organization and function?

Lamins are proteins that form a meshwork lining the inner nuclear membrane. They interact with chromosomes, helping to organize them within the nucleus. Lamins play roles in maintaining nuclear structure, regulating gene expression, and facilitating proper cell division.

43. What is crossing over and why is it important?

Crossing over is the exchange of genetic material between homologous chromosomes during meiosis. It's important because it increases genetic diversity by creating new combinations of alleles, which contributes to evolution and adaptation in populations.

44. How do chromosomal translocations occur and what are their effects?

Chromosomal translocations occur when a segment of one chromosome breaks off and attaches to another chromosome. This can lead to genetic disorders if it disrupts important genes or creates fusion genes. Some translocations are associated with certain cancers.

45. How do chromosomes behave differently in mitosis versus meiosis?

In mitosis, chromosomes replicate and separate to produce two identical daughter cells. In meiosis, chromosomes undergo two divisions: homologous chromosomes separate in the first division, and sister chromatids separate in the second, resulting in four genetically diverse haploid cells.

46. How do environmental factors influence chromosome structure and function?

Environmental factors like radiation, certain chemicals, or viruses can damage chromosomes, causing breaks or rearrangements. This can lead to mutations, affect gene expression, or cause chromosomal abnormalities. Some environmental factors can also influence epigenetic modifications on chromosomes.

47. How do chromosomes change during the cell cycle?

Chromosomes undergo significant changes during the cell cycle. They replicate during S phase, condense during prophase of mitosis or meiosis, align at the metaphase plate, and then separate to opposite poles during anaphase. They decondense again in telophase.

48. How do chromosomes contribute to genetic linkage and gene mapping?

Genes located close together on the same chromosome tend to be inherited together, a phenomenon called genetic linkage. This principle is used in gene mapping to determine the relative positions of genes on chromosomes based on how frequently they are inherited together.

49. How do chromosomes contribute to genetic anticipation in certain disorders?

Genetic anticipation, where a genetic disorder becomes more severe or appears earlier in successive generations, is often associated with expanding repeat sequences on certain chromosomes. This is seen in disorders like Huntington's disease, where a specific repeat on chromosome 4 expands over generations.

50. How do chromosomes behave differently in somatic cells versus germ cells?

In somatic cells, chromosomes undergo mitosis to produce genetically identical daughter cells. In germ cells, chromosomes undergo meiosis, which includes processes like crossing over and independent assortment, leading to genetically diverse gametes.

51. How do chromosomal abnormalities in somatic cells differ from those in germ cells in terms of their effects?

Chromosomal abnormalities in somatic cells can lead to various health issues, including cancer, but affect only the individual. Abnormalities in germ cells, however, can be passed on to offspring, potentially causing hereditary disorders or influencing evolution.

52. What is the significance of chromosome fragile sites?

Chromosome fragile sites are specific regions that tend to form gaps or breaks when cells are cultured under certain conditions. They're associated with genome instability and can be involved in chromosomal rearrangements linked to various diseases, including some cancers.

53. How do chromosomes contribute to genetic mosaicism?

Genetic mosaicism occurs when an individual has two or more genetically distinct cell populations. This can result from chromosomal abnormalities occurring during early embryonic development, leading to some cells having a different chromosomal makeup than others.

54. How do chromosomes contribute to the phenomenon of position effect variegation?

Position effect variegation occurs when a gene's expression is influenced by its position on the chromosome, particularly when it's moved near heterochromatin (tightly packed, gene-poor regions). This phenomenon highlights how chromosome structure and gene positioning can affect gene expression.