23 Chromosomes Functions and Types of Chromosomes (original) (raw)
Last Updated : 24 Jul, 2025
**Chromosomes are made of DNA molecules and are found in the nucleus of a cell. There are 23 chromosome pairs in humans. Transporting genetic information from one cell generation to the next is the main function of chromosomes. Several genes on each chromosome code for different proteins. The features of the entire organism are influenced by or determined by these genes.
Table of Content
- What are Chromosomes?
- Human Chromosome Types
- 23 Chromosomes and Their Functions
- Structure of Chromosome
- Different types of Chromosomes
- Genetic Mapping with Chromosomes
- Function of X and Y Chromosomes
What are Chromosomes?
Chromosomes are thread-like structures found in the nucleus of the cell. It is made up of DNA, histones, and other non-histone proteins. DNA (deoxyribonucleic acid) is a nucleotide sequence that carries the genetic information necessary for all living organisms' growth, development, functioning, and reproduction. Genes are made up of a sequence of DNA and is the fundamental hereditary unit.
DNA undergoes primary, secondary, and tertiary levels of packaging by wrapping around histone molecules and associated proteins to form the solenoid chromatin structure found in a resting cell's nucleus. During cell division, in the metaphase, the chromatin in the nucleus further condenses to form chromosomes.
The number of chromosomes in an organism is also species-specific. For example, humans have 23 pairs of chromosomes, while a fruit fly (Drosophila melanogaster) has four pairs of chromosomes. Chromosome was discovered by Walther Flemming.
Human Chromosome Types
In humans, each cell typically contains 23 pairs of **chromosomes. Thus, a total of 46 chromosomes are found in humans. One chromosome in each pair is inherited from the mother and the other from the father.
The 22 pairs of chromosomes are called autosomes, and the 23rd pair is called the sex or allosome chromosome. There are two types of allosomes: X and Y chromosomes. Allosomes determine an individual's sex. A person with two X chromosomes is a female (XX), and a person with one X and Y chromosome is a male (XY).
23 Chromosomes and Their Functions
Each of the 23 chromosome pairs has a distinct set of genes that codes for specific proteins. These proteins have different functions in the body and can be summarized as follows:
| Name of Chromosome Pair | Gene Present | Function | Chromosome Disorder |
|---|---|---|---|
| 1 | TP53, APP, NOTCH2, GJB3 | Regulation of cell cycle, intellectual ability, and development. | Li-Fraumeni syndrome, Alzheimer's disease. |
| 2 | BRCA2, MYCN, APPBP2 | DNA repair, Neuroblastoma. | Breast and ovarian cancer, Neuroblastoma. |
| 3 | MLH1, TP73, CREBBP | DNA repair, Apoptosis, Transcription | Lynch syndrome, Rubinstein-Taybi syndrome |
| 4 | FGFR3, EDAR, TLR3 | Development, Immune response | Achondroplasia, Hypohidrotic ectodermal dysplasia |
| 5 | APC, ADAMTS2, IRF1 | WNt signaling, Extracellular matrix | Familial adenomatous polyposis, Aortic aneurysm |
| 6 | HFE, PARK2, TBP | Iron homeostasis, Parkinson's | Hereditary hemochromatosis, Parkinson's disease |
| 7 | CFTR, BRAF, FOXP2 | Cystic fibrosis, Cell signaling | Cystic fibrosis, Williams syndrome |
| 8 | FGFR1, MYC, RAD21 | Cell growth, Transcription | Kallmann syndrome, Burkitt lymphoma |
| 9 | ABO, NOTCH1, DMRT1 | Blood type, Notch signaling | ABO blood group system, Alagille syndrome |
| 10 | PTEN, FGFR2, MXI1 | Cell cycle regulation, Development | Cowden syndrome, Craniosynostosis |
| 11 | FOLR1, ATM, WT1 | Folate metabolism, DNA repair | Cystic fibrosis, Wilms tumor |
| 12 | KIT, BRCA1, CDK4 | Cell signaling, DNA repair | Gastrointestinal stromal tumor, Breast cancer |
| 13 | RB1, BRCA2, FOXO1 | Cell cycle regulation, DNA repair | Retinoblastoma, Breast cancer |
| 14 | ADAM32, NKX2-5, PRMT5 | Spermatogenesis, Heart development | Klinefelter syndrome, Cardiac defects |
| 15 | SNRPN, UBE3A, SMAD7 | Imprinting, Ubiquitin-proteasome | Angelman syndrome, Marfan syndrome |
| 16 | CDH1, FANCA, SALL1 | Cell adhesion, DNA repair | Hereditary diffuse gastric cancer, Townes-Brocks syndrome |
| 17 | TP53, BRCA1, ERBB2 | Cell cycle regulation, Breast cancer | Li-Fraumeni syndrome, Breast cancer |
| 18 | SMAD2, DCC, PMP22 | TGF-beta signalling, Cell adhesion | Edwards syndrome, Hirschsprung's disease |
| 19 | APOE, CACNA1A, LIPC | Lipid metabolism, Ion channels | Alzheimer's disease, Familial hypercholesterolemia |
| 20 | BMP2, GNAS, TFAP2B | Bone development, G protein signalling | Albright hereditary osteodystrophy, Brachydactyly |
| 21 | APP, RUNX1, DSCR1 | Alzheimer's, Blood cell formation | Down syndrome (Trisomy of 21), Acute myeloid leukaemia |
| 22 | CHEK2, TBR1, SLC25A13 | DNA repair, Brain development | Li-Fraumeni syndrome, Citrin deficiency |
| X | XIST, FMR1, SHOX | X chromosome inactivation, Fragile X | Albright hereditary osteodystrophy, Brachydactyly |
| Y | SRY, AMELY, USP9Y | Male sex determination, Y-linked genes | Male infertility, Swyer syndrome |
Structure of Chromosome
Each chromosome is made up of three fundamental parts:
- **Chromatids: Each chromosome is made up of two sister chromatids.
- **Centromere: Two sister chromatids are joined at a point called the centromere.
- **Telomere: The ends of each chromosome are called the telomere.
- The entire set of chromosome of an organism that has been organised according to shape, size, and number is called the karyotype.
Different types of Chromosomes
Chromosomes can be classified into four types based on the position of centromeres.
- **Metacentric Chromosome: In these chromosomes, the centromere is in the middle. It gives V-shaped chromosomes.
- **Sub-Metacentric Chromosome: The centromere is slightly off-center in these chromosomes. This gives rise to L-shaped chromosomes.
- **Acrocentric Chromosome: The centromere is located towards one end, giving J-shaped chromosomes in acrocentric chromosomes.
- **Telocentric Chromosomes: In this type of chromosome, the centromere is near the end or telomere of the chromosome. This gives chromosomes an I shape.
Genetic Mapping with Chromosomes
Genetic mapping is the process of determining the location of genes on a chromosome. It is done in two ways:
**Linkage Mapping
Linkage mapping is the process by which the location of genes is determined on a chromosome based on the probability of the genes being inherited together. More linkage occurs in genes that are closer to each other.
**Physical Mapping
Physical mapping is the process by which the location of genes on a chromosome is located with the help of a specific gene marker. One of the main advantages of knowing the structure of chromosomes is **genetic mapping.
Function of X and Y Chromosomes
The X and Y chromosomes are called the sex chromosomes. Their functions are as follows:
- These chromosomes are responsible for the determination of the gender of an organism. The X and Y chromosomes encode genes that are responsible for the determination of the sex of an organism.
- In humans and bees, males are heterogametic i.e. they have one X and one Y **chromosome, while females are homogametic i.e. they have two X chromosomes.
- The Y chromosome contains the TDF (Testes determining factor) in the SRY ****(Sex-determining region of Y**) responsible for initiating male sex determination.
- On the other hand, the X chromosomes are inactivated in homogametic organisms like human females to maintain a balance between copies of genes found in the X chromosome.
Conclusion - 23 Chromosomes
In conclusion, the function of chromosomes is to carry the basic genetic material DNA. Chromosomes is made up of proteins and DNA organized into genes. Studying the 23 pairs of chromosomes and their functions is an important part of biology to understand various developmental pathways and diseases associated with these genes. With genetic mapping, one can also identify the location of genes that may be related to disease and thus help in understanding the diseases or making a target drug.
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