With the exception of the sex chromosomes, diploid eukaryotic organisms such as humans have two copies of each chromosome, one inherited from the father and one from the mother.The large amount of genomic DNA in a eukaryotic cell is tightly packaged in chromosomes contained within a specialized organelle, the nucleus.Metacentric are V-shaped chromosomes in which centromere lies in the middle of chromosome so that the two arms are almost equal.Sub-metacentric chromosomes are with centromere slightly away from the mid-point so that the two arms are unequal.One arm is very long and the other is very short. Acrocentric are also rod-shaped chromosomes with centromere occupying a sub-terminal position.Telocentric are rod-shaped chromosomes with centromere occupying the terminal position, so that the chromosome has just one arm.On the Basis of Location of Centromere Figure: Types of Chromosomes. Diffused or non-located with indistinct centromere diffused throughout the length of chromosome.Ĭ.Such chromosomes represent freshly broken segments of chromosomes which do not survive for long. Polycentric with more than two centromeres.Humans have 23 pairs of chromosomes in their cells, of which 22 pairs are autosomes and one pair of sex chromosomes, making a total of 46 chromosomes in each cell.įigure: Human Karyotype.The rest of the genetic information is present in the autosomes. Genetic traits that are linked to the sex of the person are passed on through the sex chromosomes.Human chromosomes are of two types- autosomes and sex chromosomes.(5) Secondary constriction or Nucleolar organizer, In mitotic metaphase chromosomes, the following structural feature (except chromomere) can be seen under the light microscope: Each chromonemata consists of about 8 microfibrils, each of which is formed of a double helix of DNA.The two chromonemata are also tightly coiled together that they appear as single thread of about 800A thickness.Embedded in the matrix of each chromosome are two identical, spirally coiled threads, the chromonemata.It is also formed of non-genic materials.It is the ground substance of chromosome which contains the chromonemata.It is very thin and is formed of achromatic substances.It is the outer envelope around the substance of chromosome.Structurally, each chromosome is differentiated into three parts.Each chromosome typically has one centromere and one or two arms that project from the centromere.In eukaryotes the chromosomes are multiple large, linear and are present in the nucleus of the cell.Structure of a Chromosome Structure of a Chromosome Adjacent nucleosomes are connected via “linker DNA”. Each nucleosome consists of histone octamer core, assembled from the histones H2A, H2B, H3 and H4 (or other histone variants in some cases) and a segment of DNA that wraps around the histone core.The nucleosome is the smallest structural component of chromatin and is produced through interactions between DNA and histone proteins.This is achieved through nucleosome assembly. In the first step of this process, DNA is condensed into an 11 nm fiber that represents an approximate 6-fold level of compaction.The assembly of DNA into chromatin involves a range of events, beginning with the formation of the basic unit, the nucleosome, and ultimately giving rise to a complex organization of specific domains within the nucleus.Chromatin are a highly compacted structure consisting of packaged DNA and necessary so as to fit DNA into the nucleus.The complex of both classes of protein with the nuclear DNA of eukaryotic cells is known as chromatin.The proteins that bind to the DNA to form eukaryotic chromosomes are traditionally divided into two classes: the histones and the non-histone chromosomal proteins.Each chromosome is made up of DNA tightly coiled many times around proteins that support its structure.Chromosomes are the nuclear components of the special organization, individuality, and function that are capable of self-reproduction and play a vital role in heredity, mutation, variation and evolutionary development of the species.They appear as rod-shaped dark stained bodies during the metaphase stage of mitosis when cells are stained with a suitable basic dye and viewed under a light microscope. Chromosomes were first described by Strasburger (1815), and the term ‘chromosome’ was first used by Waldeyer in 1888. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes.
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