23 Chromosomes and Their Functions

Chromosomes

A chromosome is a nucleoprotein structure that generally appears like a rod-shaped structure during nuclear division. These chromosomes are tightly packed inside the nucleus of a cell and are made of DNA molecules. This DNA is responsible for carrying the hereditary information. Thus chromosomes as a whole play an important role in inheritance.

Gene is typically a unit of DNA that is located on the chromosome in a linear fashion. The occurrence of different genes on the same chromosome is called linkage. Furthermore, all genes located physically on a given chromosome are termed a ‘linkage group’.

Human Chromosomes

In humans, 23 such chromosomes occur in pairs and thus totalling 46 chromosomes. These 23 pairs can be divided into autosomes and allosomes. The first 22 pairs come under autosomes, and the 23rd pair is the allosome or sex chromosome.

Also Read: Difference between Gene and DNA

Genetic Mapping

Geneticists use ‘map unit’ to measure the distance between linked genes. It is a diagrammatic graphical representation that displays the exact arrangement, location and combination of genes in a linkage group of chromosomes. This kind of gene mapping technique plays a vital role in the Human Genome Project (HGP). The goal of this international research project is to identify and sequence all the genes that make up the human genome.

Genetic mapping is also adopted to construct linkage maps for fungi, Drosophila, maize, garden pea, etc.

23 Chromosomes and Their Functions

The major function of chromosomes is to carry the hereditary information from one cell generation to the next. DNA is the only permanent component of the chromosome and is the sole genetic material of eukaryotes. Each chromosome has several genes that code multiple proteins. Thus they determine or influence the traits of the entire eukaryote.

With advancing research techniques, it has become possible to locate and analyse the functions of all the 23 chromosomes in humans. The following table provides the details of the gene and diseases associated with each chromosome.

Chromosome

Gene

Diseases and Disorders

1

Actin, skeletal muscle alpha chain

Pancreatic Amylase

Acid phosphatase

Cystic fibrosis antigen

Rhesus blood antigen

Xeroderma pigmentosum A

Alzheimer’s

Glaucoma

Galactosemia

Congenital hypothyroidism

Prostate cancer

Breast cancer

Parkinson disease

2

Glucagon

Elastin

Collagen Ⅲ

Collagen Ⅳ

Testis-specific ɑ tubulin

Interferon Ⅰ

Autism

Gilbert’s syndrome

Waardenburg syndrome

Brachydactyly type D

Lynch syndrome

3

Rhodopsin

Somatostatin

Lung/breast/colon/pancreatic cancer

Cataracts

Von Hippel-Lindau syndrome

4

Huntingtin protein

MN blood group

Huntington’s disease

Parkinson’s disease

Achondroplasia

5

Fibroblast growth factor, acidic

Cri du chat syndrome

Cockayne syndrome

Spinal muscular atrophy

6

Insulin-dependent diabetes mellitus 1

Β tubulin M40

Diabetes mellitus type 1

Hemochromatosis

Epilepsy

7

Histone cluster A: H1, H2A, H2B

Collagen type 1 alpha 2 chain

Non-histone chromosomal protein 2

Cystic Fibrosis

Williams syndrome

Pendred syndrome

8

Carbonic Anhydrase cluster

DNA Polymerase β

Burkitt’s lymphoma

Werner syndrome

9

ABO blood group

Tangier disease

Tuberous sclerosis

10

Hexokinase Ⅰ

Pfeiffer syndrome

Barakat syndrome

11

Insulin

Catalase

Ataxia telangiectasia

Insulin-dependent diabetes mellitus type 2

12

Collagen Ⅱ, alpha 1

Salivary protein complex

Phenylketonuria

Pallister-Killian syndrome

13

Collagen Ⅳ alpha 1 chain and alpha 2 chain

Ribosomal RNA

Patau syndrome

Retinoblastoma

Wilson’s disease

14

T-cell leukaemia 1

Immunoglobulin heavy chain gene cluster

Ribosomal RNA

Alzheimers

Burkitt’s lymphoma

Multiple myeloma

15

Ribosomal RNA

Tay-Sachs disease

Marfan syndrome

Prader-Willi syndrome

16

Nonhistone chromosomal protein 1

Haemoglobin alpha

Haemoglobin zeta

Familial Mediterranean fever

Thalassemia

17

Growth hormone

Charcot-Marie-Tooth disease

18

Gastric releasing peptide

Niemann-Pick disease

19

Green/blue eye colour

Bombay phenotype

Myotonic dystrophy

Maple syrup urine disease

20

Growth hormone-releasing factor, somatocrinin

Alagille syndrome

21

Ribosomal RNA

Down syndrome

Autoimmune polyendocrine syndrome

22

Ribosomal RNA

Myoglobin

DiGeorge syndrome

Chronic myeloid leukaemia

X

Haemophilia A, factor Ⅷ

Haemophilia B, factor Ⅸ

Gonadal dysgenesis, XY female type

Turner syndrome

Rett syndrome

Haemophilia A

Y

Pseudoautosomal segment

Testicular determining factor

Azoospermia-third factor

H-Y antigen

Y chromosome microdeletion

XYY syndrome

As mentioned earlier, each chromosome has several genes. The above table discusses a few genes and a few disorders associated with each chromosome.

Function of X and Y chromosomes

In humans, the X chromosome has about 800 protein-coding genes and the Y chromosome has about 70 genes. Both males and females have X chromosomes – males have one X whereas females have two X chromosomes. The X chromosome also has a role in moulding sex-specific immune responses. Whereas the Y chromosome carries a unique gene called the SRY gene that initiates the sex determination in males. It is also known as the testis-determining factor.

Also Check: Difference between Gene and Chromosome

Frequently Asked Questions

What is the difference between autosomes and allosomes?

Autosomes are chromosomes that are labelled with numbers from 1 to 22. They determine the somatic traits. Whereas allosomes are sex-determining chromosomes. They are the 23rd pair and are labelled as XY, ZW, ZO and XO. Autosomes and the female allosomes (XX) are homologous and the male allosomes are non-homologous (XY).

What are karyotype and idiogram?

A karyotype is the entire set of chromosomes of a cell or individual, as seen during mitotic metaphase. It helps to determine the size, shape, number and type of chromosomes. Idiogram is nothing but the diagrammatic representation of a karyotype. Usually, in an idiogram, the chromosomes of a haploid set of an organism are ordered in a series of decreasing sizes.

What is cytological mapping?

Cytological maps or physical maps determine the physical locations of a gene in a chromosome with the help of genetic markers. Cytological maps are more accurate in terms of genome representation than genetic maps. The genetic map provides insight into the nature of various regions of the chromosome and is comparatively less efficient.

Keep exploring BYJU’S Biology for more exciting topics

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