Cell Biology

Chromosome Definition, Function, Structure, Types

Chromosomes are a collection of tightly coiled DNA that are located in the nucleus of virtually every cell of our body. Humans...

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This article writter by MN Editors on March 01, 2022

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Chromosome Definition, Function, Structure, Types
Chromosome Definition, Function, Structure, Types

What is a chromosome?

Chromosomes are a collection of tightly coiled DNA that are located in the nucleus of virtually every cell of our body. Humans possess 23 chromosome pairs.

  • The term chromosome originates from the Greek chroma, which means “colour” and”soma”, and “body” which refers to the strong staining they get from certain dyes.
  • The term was invented by the German Anatomist Heinrich Wilhelm Waldeyer, referring to the term chromatin which was invented by Walther Flemming, who was the first to discover the process of cell division.
  • Certain of the earlier words in karyology have been deemed obsolete. For instance, Chromatin (Flemming 1880) and Chromosom (Waldeyer 1888) Both attribute the color of a state that is not colored.
  • In animal and plant cells DNA is tightly packed into thread-like structures, referred to as”chromosomes. This is different from bacteria, where DNA is floating freely within the cell.
  • One length of DNA is wrapped multiple times over a variety of proteins, known as histones to create structures known as nucleosomes.
  • These nucleosomes then wrap tightly to form loops of chromatin.
  • The chromatin loops are connected to create a complete chromosome.
  • Every chromosome has two arms that are short (p arms) as well as two more long arms (q arms) and a centromere that holds the entire thing together in the center.
  • Humans have 23 pairs chromosomes (46 in all) One set comes from your mother while another set is from your father.
  • Of the 23 pairs, only one pair is a sex chromosome, meaning that they will differ in the case of gender-neutral or female (XX for females as well as XY for males).
  • The remaining 22 pair are called autosomes (non-sex chromosomes) and are the same for females and males.
  • The DNA that makes up every chromosome in our bodies is made up of many thousands of genes.
  • The ends of each chromosome are DNA fragments known as Telomeres. Telomeres shield the ends of chromosomes when DNA replication occurs by forming an elongated cap, similar to the tip of a plastic shoelace.
  • The majority of eukaryotic DNA chromosomes have packaging proteins known as histones that are assisted by chaperone proteins, connect to and expand the DNA molecule, ensuring its integrity. The chromosomes exhibit a complex three-dimensional structurethat plays an important part in the regulation of transcription.
  • Chromosomes appear under a microscope light only during the metaphase phase of the cell’s division (where all chromosomes are aligned to the middle of the cell , in their compressed version). In the beginning every chromosome is duplicated (S phase) and each copy is joined by an X-shaped centromere. This results in an shape-like structure called an X (pictured above) depending on whether the centromere is located in equatorially or in an arm-like structure when the centromere is situated further distally. The copies that are joined are known as sister chromatids.
  • In metaphase, the X-shaped structure is referred to as a metaphase chromosome. This is highly condensed , making it easier to identify and examine.
  • In animals, chromosomes achieve their maximum compaction in anaphase in chromosome segregation.
  • Chromosomal meiosis and later sexual reproduction plays a major part in the genetic diversity. In the event that these structure are controlled in a way that is not correct, such as chromosomal instability or translocation the cell could suffer a mitotic catastrophe. This will usually cause cells undergo apoptosis, leading to the death of the cell however, sometimes mutations within cells can block the process and cause the growth of cancer.
  • Certain people use the term chromosome in a broad sense to refer to the unique parts of chromatin found in cells, which are visible or not when using light microscope. Some use the term in a narrower sense to mean the distinct parts of chromatin that occur in cell division that are visible with light microscopes because of high condensation.
Illustration showing how DNA is packaged into a chromosome.
Illustration showing how DNA is packaged into a chromosome. | Image credit: Genome Research Limited

Features of eukaryotic chromosome

  • Chromosomes are most visible in metaphase.
  • Chromosomes carry the genes in a linear way.
  • Chromosomes can vary in size, shape and the number of them in different species of animals and plants.
  • Chromosomes possess the property of self-duplication and mutation.
  • Chromosomes consist comprised of DNA,RNA and proteins.

Size of Chromosome 

  • The size of chromosomes is measured in mitotic metaphase, usually measured in length and dia
  • The Chromosome of plants is usually longer than animals.
  • Plant Chromosomes typically measure 0.8-7um in length, whereas animals’ chromosomes range from 0.5-4um in length.
  • Chromosomes ‘ size vary between species

Shape of Chromosome 

  • The shape of the chromosome is typically determined by the location of the centromere.
  • The chromosomes typically exit in three different forms such as. rod shape, V shape, and J shape.

Chromosome structure

Structurally , chromosomes consist of seven components

Chromosome structure
Diagram of a replicated and condensed metaphase eukaryotic chromosome. (1) Chromatid – one of the two identical parts of the chromosome after S phase. (2) Centromere – the point where the two chromatids touch. (3) Short arm (p). (4) Long arm (q). | Image Source: https://en.wikipedia.org/wiki/File:Chromosome.svg
  1. Centromere: It’s an area of the chromosome to which spindle fibers are connected. This is known as primary constriction or centromere or Kinetochore.
  2. Chromatid: One of two distinct longitudinal subunits that make up the chromosome, is known as chromatid. Chromatids come in two varieties: sister chromatids as well as non sister chromatids.
  3. Secondary constriction: Certain chromosomes has secondary constriction along with primary constriction. The chromosomal region that lies between telomeres is known as a trapant or satellite. The chromosome that has satellites is referred to”satellite chromosome.
  4. Telomere: Telomeres are the two sides of a the chromosome are referred to as Telomeres. Telomeres are extremely stable and do not connect or join with telomeres of the other chromosome.
  5. Chromomere: The chromosomes in certain species have tiny beads-like structures known as Chromomeres. The chromomere structure in the chromosome remains always the same.
  6. Chromonema: Threadlike coils found in chromosomes and chromatids are referred to as the chromonema (plural the term chromonemata).
  7. Matrix: It’s an element of fluid that contains chromonemata. It is referred to as matrix.

Chemical composition of chromosome

Chemically chromosomes are nucleoproteins, which in nature, which means they are made up of DNA, RNA and protein. In general, chromosomes have 30-40 50% DNA, 50-65 percent protein, and 0.5to 10 percent DNA

DNA

There is a lot of DNA that is present in the somatic cells is constant. The DNA content of gametic cells is about half the somatic cell. The DNA in chromosomes are comprised of two kinds: i) Unique DNA and ii) Repetitive DNA

  • Unique DNA: unique DNA is made up of the DNA sequences that exist in only one DNA copy and are unique in the world of. It is referred to as non-repetitive DNA. Codes for proteins that must be present huge quantities for the cell. eg- storage protein.
  • Repetitive DNA: Repetitive DNA comprises DNA nucleotides or base sequences that can be as little as a few hundred bases (bp) long and comprised of up millions of copies within a genome. Human genome contains 30% repetitive DNA. Repetitive DNA can further be divided into
    • Highly repetitive DNA, and
    • Moderately repetitive DNA

RNA

Purified chromatin contain 10-15% RNA. The chromosome-associated RNA comprises messenger transcript RNA, transfer RNA as well as the ribosomal RNA.

Protein

The chromosome-associated protein is divided into two broad categories;

  • Histone or the protein of base
  • Non-histone proteins (Non histone protein) is acidic. histone proteins are fundamental in nature due to basic amino acids)

i) Histone protein

histones comprise around 80% of overall chromosomal proteins. They’re found in a close proportion to DNA. Five histone fractions are present, including 1H1, 2H2a and 2H2b, 2H3 , and 2H4.

ii) Non histone protein

Non histone proteins constitute up 20 percent of entire protein weight. The composition of non histone protein differs from species to species. Non histone protein is comprised of several important enzymes such as DNA and RNA polymerase.

Chromatin

Within a cell DNA doesn’t usually exist on its own, however, it’s a part of specific proteins that help organize it and provide it with shape. In eukaryotes they have proteins that include the histones. They are a collection of base (positively chargeable) proteins that create “bobbins” around DNA, which negatively charged DNA could be wrapped. Apart from organizing DNA, and making it less bulky histones play an essential function in determining which genes are in active. The combination of DNA with histones and structural proteins is known as Chromin.

In the majority of the time in the cells, chromatin becomes decondensed. It is found in thin, long strings that appear like tiny squiggles in the microscope. In this condition, DNA is accessed quickly by cell machines (such in the form of proteins which can read and replicate DNA) and is crucial for allowing cells to develop and function.

Decondensed might seem like an odd name for this kind of state but why not just label it “stringy”? However, it makes sense once you realize that chromatin also has the ability to condense. Condensation occurs as cells are nearing the point of division. When chromatin is condensed it is clear that the DNA of eukaryotic cells is not only one long string. It’s actually broken into distinct linear pieces, referred to as the chromosomes. Bacteria also have chromosomes but their chromosomes tend to be circular.

Chromatin
Chromatin | Image Source: https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cycle/cell-cycle/a/dna-and-chromosomes-article

Duplication of Chromosome 

Chromosome duplication happens before the division process of mitosis as well as meiosis. DNA replication processes permit the correct chromosome number to be maintained after the original cell splits. A duplicated chromosome comprises by two identical chromosomes, referred to as sister chromatids, which are linked to the center of the centromere. Sister chromatids stay together until the conclusion in the process of division, when the spindle fibers separate them, and then encased inside separate cells. After the paired chromatids are separated and are separated from each other it is the case that each is called an chromosome daughter.

Chromosomes and cell division

One of the key aspects of effective cell division involves the right distribution of the chromosomes. When mitosis is occurring, this implies that chromosomes need to be divided between two cells. In meiosis, the chromosomes have to be split between four cells. The cell’s spindle apparatus the one responsible for shifting chromosomes in cell division. This kind of cell movement results from interaction between microtubules of the spindle as well as motor proteins, which work in tandem to control and separate the chromosomes.

It is crucial that the correct amount of chromosomes is maintained within cells that divide. Incorrect cell division could cause people to have imbalanced number of chromosomes. The cells could have too many or too few chromosomes. This kind of situation can be referred to as aneuploidy. It can occur in the autosomal chromosomes that occur during mitosis, or in sex chromosomes that are formed during meiosis. Aneuploidies in chromosomes could cause birth problems, developmental disabilities, and even death.

Chromosomes and Protein Production

Protein production is an essential cell function that depends on DNA and chromosomes. Proteins are essential molecules that are essential to perform a variety of functions of the cell. Chromosomal DNA has segments that are genes that encode for proteins. When proteins are produced the DNA is unwinded along with its codifying segments. These segments are translated into an transcript of RNA. The DNA information is then transferred from the nucleus, and later transformed into proteins. Ribosomes as well as another DNA molecule, referred to as transfer RNA, collaborate to connect to the transcript of RNA and transform the encoded message into proteins.

Mutation of Chromosome

Chromosome changes are the modifications that occur on the chromosomes. They are usually due to either errors that occur during meiosis or exposure to mutagens like radiation or chemicals. Chromosome breakage or duplications may result in a variety of structural changes in chromosomes which tend to be harmful to the person. These kinds of mutations cause some chromosomes that have additional genes, insufficient genes, or those that are located in the wrong sequence. Mutations can also result in cells with abnormal amounts of the chromosomes. The abnormal chromosome number usually occurs due to disjunction, or failure of homologous chromosomes correctly during meiosis.

Types of Chromosomes

Types of Chromosomes Based on the Location of Centromere

1. Metacentric Chromosomes

Metacentric chromosomes include the centromere located in the middle which means that each section is of equal length. Human chromosomes 3 and 1 are both metacentric.

2. Submetacentric Chromosomes

Submetacentric chromosomes are those with the centromere that is slightly offset from its center, leading to an asymmetry of both sections’ lengths. Human chromosomes 4 to 12 are submetacentric.

3. Acrocentric Chromosomes

Acrocentric chromosomes possess one centromere, which is off from the center, which results in a very long and a extremely short segment. Human chromosomes 13,15 21 and 22 are Acrocentric.

4. Telocentric Chromosomes

Telocentric chromosomes contain the centromere located at the at the end of the genome. Humans don’t have Telocentric chromosomes however they can be present in other species, like mice.

Types of Chromosomes Based on the Location of Centromere
Types of Chromosomes Based on the Location of Centromere

Types of Chromosomes Based on the Number of Centromeres

Based on the number of Centromeres the chromosomes are divided into five groups as;

  1. Monocentric: Monocentricchromosomes are those that have just one centromere.
  2. Dicentric: Dicentric chromosomes contain two centromeres.
  3. Polycentric: Polycentricchromosomes include at least two centromeres
  4. Acentric: They lack a centromeres. These chromosomes are freshly broken chromosomes that don’t last long.
  5. Non-located or Diffused: Diffused or non-located chromosomes have an indistinct centromeres spread across the length of the chromosome.

Chromosomes can also be classified into two categories , such as

  1. Chromosomes for sexual chromosomes
  2. Autosome

Autosome

An autosome is a type of chromosome that isn’t one of the sex chromosomes. The autosome members in a pair within diploid cells share similar morphologies, but differ from the allosomes that might differ in structure. The DNA found in autosomes is collectively referred to in the form of atDNA also known as auDNA.

For instance, humans are a diploid species with a genome that typically has the autosomes of 22 pair as well as an allosome pairing (46 chromosomes in total). The autosome pairs are identified by numerals (1-22 for human beings) roughly in the order of their size in base pairs, whereas allosomes are identified by their initials. In contrast, the allosome pair is composed of two X-chromosomes in females, or one X as well as one Y chromosome for males. Strange combinations of XYY various XXY and XXXXXX in addition to others Salome variations, are widely known to happen and often result in developmental anomalies.

Autosomes are still populated with sexuality-related genes, even though they’re not sex-chromosomes. For instance the SRY gene located on the Y genome encodes the transcription factor TDF and is essential in determining male sex throughout the development. TDF acts by activating the SOX9 gene on chromosome 17 and mutations in the SOX9 gene may cause human beings with a normal Y chromosome to become females.

autosomal recessive gene
autosomal recessive gene | Image Source: https://en.wikipedia.org/wiki/Autosome#/media/File:Autosomal_recessive_inheritance.gif

Autosomes from all human species have been identified and mapped using the chromosomes of cells caught in metaphase or in prometaphase, and staining them using a particular dye (most frequently, Giemsa). These chromosomes can be usually regarded as karyograms for simple comparison. Geneticists in clinical research can compare the karyograms of an individual with a reference karyogram in order to identify the cytogenetic causes of specific characteristics. For instance the karyograms of someone who suffers from Patau Syndrome could reveal that they have three copies of the 13th chromosome. Karyograms and staining techniques can only detect large-scale disruptions to chromosomes–chromosomal aberrations smaller than a few million base pairs generally cannot be seen on a karyogram.

Sex chromosome

A sexchromosome (also known as an allosome, heterotypical or heterotypical chromosome or heterochromosome) or an idiochromosome) is a chromosome which is distinct from the normal autosome with regard to form size, shape, and behavior. Human sex chromosomes comprise a typical pair of mammal’s allosomes determine the gender of an individual who is created through sexual reproduction. Autosomes are different from allosomes in that autosomes are found in pairs where members have the same structure however they different from the other pair within an allopolyploid cell. In contrast, individuals of an pairing might vary from the other and determine the sex.

Nettie Stevens, and Edmund Beecher Wilson both independently discovered sex chromosomes around 1905. But, Stevens is credited for finding these prior to Wilson.

Prokaryotic Chromosomes

  • The prokaryote genome is typically comprised of one chromosome and plasmids.
  • Eukaryota have more chromosomes. We can distinguish two kinds of eukaryota’s mitochondrial kind of chromosomes (nuclear as well as mitochondrial) and, sometimes, even plasma plasmids.
  • Prokaryotic chromosomes can be found in the nucleoid of prokaryotic cells and are circular in shape.
  • Contrary to eukaryotic cells cell do not possess a nucleus that is membrane-bound. Instead their genetic material can be found in a portion in the cytoplasm, known as the nucleoid.
  • A prokaryotic cells typically is composed of a single circular chromosome that is coiled. There are however some prokaryotes with more than one. Vibrio cholerae, the bacterium responsible for the cholera outbreak has two circular chromosomes.
  • Every chromosome is home to DNA molecules that is supercoiled and compressed by nucleoid-associated protein (NAPs).
  • Prokaryotic cells could have only one chromosome. However, the chromosome that is one is a long DNA molecule that has to be compacted to fit in the tiny space. In a cell that is eukaryotic, DNA wraps around clusters histone proteins. But, the majority of prokaryotic cells aren’t using histones to aid in storage of DNA. (Some Archaea do, but they’re the exception instead of the norm.)
  • Similar to eukaryotic DNA and prokaryotic DNA is subjected to supercoiling but it’s not wrapped around histone clusters before. Supercoiling employs the use of tension to bend a DNA molecule and wrap it around itself and creates loops.
  • Folding of DNA in prokaryotic cells is made easier by nucleoid-associated protein (NAPs) rather than histones. NAPs are proteins found within the nucleoid, which can attach to DNA molecules by causing folds and bends and are associated in processes like transcription and replication of DNA.
  • The Prokaryotic cell is haploid that is, they don’t possess homologous chromosomes. pairs.
  • The majority of prokaryotic cells only have one chromosome. They have been classified as having haploid cell (1n with no the chromosomes that are paired). However, in Vibrio Cholerae, which has two chromosomes, they are distinct from each other. They are not homologous since they do not have identical genes at the same places.
  • Prokaryotes, like bacteria, reproduce through binary fission. This is an method of sexual reproduction that is comparable in the end result to mitosis, where two daughter cells are created and each has the same number of chromosomes that the parent cell. When bacteria undergo binary fissions, no mitotic spindle develops. Furthermore reproduction of the cell’s genome is possible during the fission process.
  • Prokaryotic cells also contain small DNA molecules called plasmids.
  • Plasmids are tiny, circular DNA molecules that carry the cell’s essential genes. Though plasmids come in a range of dimensions (ranging from a few thousand base pairs up to several hundred thousand) They typically contain a handful of genes. Resistance to antibiotics is a characteristic that is usually attributable to plasmid genes.
  • The genetic material in plasmids is distinct from the cell’s main chromosome and they can reproduce independently of the chromosome. If a prokaryotic cell that has an plasmid divides, daughters cells each get an identical copy of the plasmid and its regular chromosome.

Eukaryotic Chromosome

  • Eukaryotic chromosomes can be found within the nucleus of cells.
  • The main characteristic that differentiates the eukaryotic from the prokaryotic cells is that it has the membrane-bound nucleus.
  • The nucleus is the “control central” within the cells. It holds all the cells’ genetic information known as DNA. Its nuclear membrane also known as the nuclear envelope, has pores, or channels that regulate molecular movement inside and out of the nucleus.
  • The DNA in the nucleus is organised into chromosomes.
  • In the simplest sense the chromosome is a DNA-based molecule which is tightly wrapped around proteins known as histones. Eukaryotic cells contain many chromosomes that are linear in their shape.
  • Each chromosome has an atom of DNA which is tightly wrapped around histone protein clusters.
  • DNA molecules are incredibly large, containing million of base pairs (matched nucleotides) each. What is the process that cells use to store these huge and bulky molecules? Like you would put thread or yarn on a spool. DNA is compressed in a coiled form, then folded into a compact size.
  • As a eukaryotic cell divides, each chromosome copies creating the identical twin chromatids that are joined together in length, with the strongest link through the centrromere.

Differences Between Eukaryotic Chromosome and Prokaryotic Chromosomes

  • The majority of eukaryotic cells have several linear chromosomes. However, prokaryotic cells possess only one circular chromosome.
  • Eukaryotic chromosomes reside in the nucleus, while prokaryotic chromosomes reside within the nucleoid.
  • In eukaryotic chromosomes DNA is wrapped around proteins called histones, and later, it’s further compacted through the process of supercoiling as well as folding. In prokaryotic chromosomes DNA is supercoiled and pressed with nucleoid proteins.
 Eukaryotic ChromosomeProkaryotic Chromosome
ShapeLinearCircular
SizeLargeSmall
NumberMultipleSingle
LocationNucleusNucleoid (region in cytoplasm)
Storage proteinsHistonesNucleoid-associated proteins

Models Proposed for Chromosome Structure

The following paragraphs outline the top four models that have been proposed to model chromosome structure. The models are: 1. Molecular Model 2. Multi-Stranded Model or Polyneme Chromosome Model 3. General Chromosome Model 4. Folded Fibre Model.

1. Molecular Model

The model of chromosome structure was developed by Taylor and his coworkers in 1957 in 1963. It is built on the semiconservative replication of the eukaryotic chromosome. According to this model the chromatid is comprised of one DNA chain, with numerous DNA double helices are joined end-to-end with proteins.

Protein molecules’ interactions with each other result in coiling and uncoiling of chromosomes. DNA molecules is broken by deoxyribonucleases however not by proteolytic enzymes.

2. Multi-Stranded Model or Polyneme Chromosome Model

This theory was first proposed by Ris in the year 1961, and by Ris along with Chandler after 1963. Based on this model, the chromosome has multi-stranded DNA, i.e. it has numerous DNA double helices, which are placed in a parallel fashion to one another. Each chromosome is separated into two chromatids. Each chromatid is composed up of 2 “half of chromatids” as well as each half-chromatid is made up from two “quarter quarter chromatids.”

Every “quarter of a chromatid” is comprised of four chromatin fibers and each fibre of chromatin has 2 DNA double helices. The size of the double DNA helix is about 2 nanometers as well as two DNA molecules join with proteins to form the chromatin fiber.

The dimensions of chromatin fibres quarter chromatids and half chromatids and chromatids range from 10 nm 40 nm 40 nm 80 num, and 160 nm according to. So, each chromatid is comprised of 32 DNA molecules, whereas the metaphase chromosome has 64 DNA molecules. But, according to recent research the chromosome is not multi-stranded.

3. General Chromosome Model

The idea was put forward by Crick in 1971. It implies that DNA in the chromatid is a huge monomer that flows all the way between one side and another. The interband and bands of the chromosomes (especially gigantic chromosomes) are thought to serve different purposes. The bands are populated with global control DNA, whereas the inter-bands are filled with the fibrous DNA that codes for proteins.

4. Folded Fibre Model

DuPraw in the year 1965 developed this model based on of studies using electron microscopy of the human chromosomes. Based on this model, every chromatid is composed of a single long nucleoprotein complex (Chromatin fibers) with one DNA double helix is the primary arrangement of the axis. The chromosome model is widely accepted.

The most important characteristics that this model has are:

  1. Prior to interphase replication, every chromosome is made up of one chromatid composed of one 500-200 A thick chromatin fibre every fibre has a large DNA double-helix, which is linked to proteins as well as RNA.
  2. The chromatin fiber (chromatid) reproduces in the S phase of the call cycle to produce two sister chromatids , which are held together by non-replicated regions.
  3. The sister chromatids are folded together to form a clear chromosome in prophase. sister chromatids remain joined by tiny un-replicated regions.
  4. Specific folding patterns as well as packing pattern of chromatids from various chromosomes is believed to differ in certain ways. Therefore, each metaphase chromatid comprised of a tightly folded one chromatin fiber that ranges from 200 to 500 A diameter. The exact 3-dimensional structure of the nucleoprotein fibre within each chromatid isn’t the same. This configuration changes from interphase to metaphase.

It can also be different from the same chromosome through meiosis and mitosis, in mature sperm, and also from the metaphase phase to the metaphase. The non-homologous chromosomes vary not just in their genetic content , but as well in their 3-dimensional layouts.

The model suggests that, in the region of the centromeric the chromatin fibres are continuous and move between one arm and another for every sister chromatid. the sister chromatids stay tightly together in this region until the point of their separation in anaphase. The model also suggests that some DNA is synthesized before sister chromatids split. The diagrammatic illustration of the model with folded fibres is shown in Fig. 8.2.

The chromatin fibers are thought to be composed of “A” or “B” types. The type A fibre lies in between the DNA double helix extended as well as the B type fully packed fibre. The DNA double helix measures approximately 20 A in diameter. It joins with histones to create nucleohistone fibrils.

The fibril is folded into super-helix with 100 A diameter and 120 A This is the kind of A fiber. The 100 A fiber folds due to the divalent effects of cations (Ca2+ Mg2+, Ca2+) in order to form an elongated system consisting comprising 250 A fibers.

The fibre that is packed fully is between 200 and 500 A in size. It is referred to as a B type fibre. When Mg2+ and Ca2++ are eliminated The 200-500 A fibers expand to form 100 A-fibrils. The process of digestion of the 100 A fibrils is accomplished by enzymes called proteinase. This results in an unidirectional 20-30 A thick stand (DNA double Helix) which is susceptible DNAase.

Function of Chromosomes

First time ever, Sutton as well as Bover suggested the importance of chromosomes for the process of heredity in 1902.

  • The primary purpose of chromosomes is to carry the most fundamental genetic material called DNA. DNA contains genetic information for many cell functions. These functions are crucial to the survival, growth and reproduction of organisms.
  • Histones and other proteins protect the Chromosomes. They protect them from damage caused by chemical (e.g. enzymes) as well as physical force. Therefore, chromosomes perform the role of protecting gene material (DNA) from harm in the course that is cell division.
  • Humans are blessed with 23 pairs of chromosomes of one of which is the sexchromosome. Females have two X-chromosomes while males have just one the Y and X chromosomes. The gender for the baby is determined by the number of chromosomes carried down by male. If X chromosomes are passed through XY, it will become female. If the Y chromosome is passed, a male develops.
  • In the course of cell division the spindle fibers connected to centromeres expand and serve a vital role. The contraction of the centromeres of the chromosomes assures a an exact dispersal of DNA (genetic material) to the nuclei of the daughter.
  • The chromosomes regulate how proteins are that are formed within our bodies and keep the order of DNA. The proteins are stored inside the coiled structure the chromosomes. The proteins that are bound to DNA aid in the proper packing of DNA.
  • Chromosomes ensure the success of division of cells throughout dieosis. The chromosomes of parent cells make sure that the right information is passed to daughter cells needed by the cell in order to grow and develop in a correct manner.
  • Chromosomes contain both histone as well as non-histone protein. these proteins regulate gene action. Cellular proteins that regulate genes function in a way by activating and deactivating the proteins. The process of activation and deactivation can either will expand or expand the chromosome.
  • Chromosomes contain the genetic material needed by the organism in order to grow and develop. DNA molecules are comprised from a series of units known as genes. Genes are the parts of DNA that encode for the specific proteins needed by cells for their optimal functioning.

Number of chromosomes of different eukaryotes

OrganismDiploid number of chromosomes (2n)Number of chromosomes
Humans2346
Earthworm1836
Dogs3978
Lily1224
Frog1326
Turkey4182
Shrimp127254
Chimpanzee2448
Potato
(Solanum  tuberosum)
2448
Hare2448
Zebrafish
(Danio rerio)
2550
Water buffalo (Riverine type) (Bubalus bubalis)2550
Striped skunk(Mephitis mephitis)2550
Pineapple
(Ananas comosus)
2550
Giraffe
(Giraffa camelopardalis)
1530
Pistachio
(Pistacia vera)
1530
Sunflower
(Helianthus annuus)
1734
Porcupine
(Erethizon dorsatum)
1734
Peanut
(Arachis hypogaea)
2040
American beaver
(Castor canadensis)
2040
Wheat
(Triticum aestivum)
2142
Rhesus monkey
(Macaca mulatta)
2142
Rat
(Rattus norvegicus)
2142
Oats
(Avena sativa)
2142
Giant panda
(Ailuropoda melanoleuca)
2142
Strawberry
(Fragaria × ananassa)
2856
Elephant
(Elephantidae)
2856
Goat
(Capra hircus)
3060
Donkey
(Equus asinus)
3162
Guinea pig
(Cavia porcellus)
3264
Horse
(Equus caballus)
3264
Sloth bear
(Melursus ursinus)
3774
Polar bear
(Ursus maritimus)
3774
Dove
(Columbidae)
3978
Chicken
(Gallus gallus domesticus)
3978
Sugarcane
(Saccharum officinarum)
4080
Crucian carp
(Carassius carassius)
50100
Kamraj (fern)
(Helminthostachys zeylanica)
4794
Rattlesnake fern
(Botrypus virginianus)
92184
Black mulberry
(Morus nigra)
154308 (highest amongst plants)

References

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  • https://www.toppr.com/guides/molecular-genetics/chromosome/
  • https://en.wikipedia.org/wiki/Sex_chromosome
  • https://en.wikipedia.org/wiki/Autosome
  • https://www.wikilectures.eu/w/Prokaryotic_Chromosomes
  • https://sciencing.com/list-five-characteristics-chromosomes-8469780.html
  • https://www.visiblebody.com/learn/biology/dna-chromosomes/prokaryotic-chromosomes
  • https://geneticeducation.co.in/prokaryotic-chromosome-definition-structure-and-function/
  • https://www.visiblebody.com/learn/biology/dna-chromosomes/eukaryotic-vs-prokaryotic
  • https://www.biologydiscussion.com/chromosomes/eukaryotic-chromosomes/models-proposed-for-chromosome-structure/36093
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