Morphology:
Size: The size of chromosome is normally measured at mitotic metaphase and may be as short as 0.25μm in fungi and birds to as long as 30 μm in some plants such as Trillium. However, most mitotic chromosome falls in the range of 3μm in Drosophila to 5μm in man and 8-12μm in maize. The monocots contain large sized chromosomes as compared to dicots. Organisms with less number of chromosomes contain comparatively large sized chromosomes. The chromosomes in set vary in size.

Shape: The shape of the chromosome changes from phase to phase in the continuous process of cell growth and cell division. During the resting/interphase stage of the cell, the chromosomes occur in the form of thin, coiled, elastic and contractile, thread like stainable structures, the chromatin threads. In the metaphase and the anaphase, the chromosome becomes thick and filamentous. Each chromosome contains a clear zone, known as centromere or kinetochore, along their length. The centromere divides the chromosome into two parts and each part is called chromosome arm. The position of centromere varies from chromosome to chromosome providing it a different shape. They could be telocentric (centromere on the proximal end of the chromosome), acrocentric (centromere at one end giving it a very short and another long arm), submetacentric (J or L shaped chromosome with the centromere near the centre), metacentric (v shaped with centromere at the centre).

Structure of Chromosome: A chromosome at mitotic metaphase consists of two symmetrical structures called chromatids. Each chromatid contains a single DNA molecule and both chromatids are attached to each other by centromere and become separated at the beginning of anaphase. The chromomeres are bead like accumulations of chromatin material that are sometimes visible along interphase chromosomes. The chromomere bearing chromatin has an appearance of a necklace in which several beads occur on a string. Chromomeres are regions of tightly folded DNA and become especially prominent in polytene chromosomes. Centromere in a chromosome contain specific DNA sequences with special proteins bound to them, forming a disc shaped structure, called kinetochore. In electron microscope the kinetochore appears as a plate or cup like disc, 0.20-0.25 nm, in diameter situated upon the primary constriction or centromere. The chromosomes of most organisms contain only one centromere and are known as monocentric chromosomes. Some species have diffused centromeres, with microtubules attached along the length of the chromosomes and are termed holocentric chromosomes. Chromosomes of Ascaris megalocephala are examples of diffused centromeric chromosomes. Telomere is the chromosomal ends which prevents other chromosomal segments to be fused with it. Besides the primary constrictions or centromeres, chromosomes also posses secondary constriction at any point of the chromosome and are constant in their position and extent. These constrictions are helpful in identifying particular chromosomes in a set. Chromosomes also contain nucleolar organizers which are certain secondary constrictions that contain the genes coding for 5.8S, 18S and 28S ribosomal RNA and induce the formation of nucleoli. Sometimes the chromosomes bear round, elongated or knob like appendages known as satellites. The satellite remains connected with the rest of the chromosomes by a thin chromatin filament.

Chromatin:
Chemical composition of chromatin
Chromatin consists of DNA, RNA and protein. The protein of chromatin could be of two types: histones and non histones.

DNA: DNA is the most important chemical component of chromatin, since it plays central role of controlling heredity and is most conveniently measured in picograms. In addition to describing the genome of an organism by its number of chromosomes, it is also described by the amount of DNA in a haploid cell. This is usually expressed as the amount of DNA per haploid cell (usually expressed as picograms) or the number of kilobases per haploid cell and is called the C value. This is constant for all cells of a species. For diploid cells it is 2C. Extending the C value we reach the C-value paradox. One immediate feature of eukaryotic organisms highlights a specific anomaly that was detected early in molecular research. Even though eukaryotic organisms appear to have 2-10 times as many genes as prokaryotes, they have many orders of magnitude more DNA in the cell. Furthermore, the amount of DNA per genome is correlated not with the presumed evolutionary complexity of a species. This is stated as the C value paradox: the amount of DNA in the haploid cell of an organism is not related to its evolutionary complexity. Lower eukaryotes in general have less DNA, such as nematode Caenorhabditis elegans which has 20 times more DNA than E. coli . Vertebrates have greaer DNA content about 3pg, in general about 700 times more than E. coli . Salamander Amphiuma has a very high DNA content of about 84pg. Man has about 3pg of DNA per haploid genome.

Histones: Histones are basic proteins as they are enriched with basic proteins arginine and lysine. At physiological pH they are cationic and can interact with anionic nucleic acids. They form a highly condensed structure. The histones are of five types called H1, H2A H2B, H3, and H4-which are very similar among different species of eukaryotes and have been highly conserved during evolution. H1 is the least conserved among all and is also loosely bound with DNA. H1 histone is absent in Sacharomyces cerevisiae.