CHROMOSOMAL ORGANISATION (Chroma-colour, soma-body)

  • Discover by – Strasburg 1875/ Darlington/ Walther Flemming in 1882
  • Name – Waldeyer 1888
  • These are the genetic material which are present in nucleus
  • It can be seen in Metaphase stag of cell division
  • It made up of DNA and the genetic carrier gene are present on it
  • These are capable to self replication.
  • These are transmit genetic material form one generation to another generation by the genes, these are called genetic carrier


  • All animals have a characteristic number of chromosomes in their body cells called the diploid (or 2n) number. This (2N) No. is fixed in all spp
  • These occur as homologous pairs, one member of each pair having been acquired from the gamete of one of the two parents of the individual whose cells are being examined.
  • At the time of gametes formation, their number remain half (N), that become 2N again after fertilization.
  • Eg- Onion (2N)=16 N= 8Human 2N = 46 N= 23 Zea mays 2N= 20 N=10 Tomato 2N=24 N=12 Potato 2N= 78, Wheat 2N= 42 Cotton 2N= 52 Cabbage = 2N 18  




The following material are present in the Eukaryotic Chromosome

  • 1 DNA
  • 2 RNA
  • 3 Protein (A) Histone (B) Non Histone
  • 4 Ca, Fe, Mg, Zn.
  • The chemical composition is different in all the stage of cell division.
  • E.g.- During the Metaphase stage DNA- 15-20% RNA 10-15% and Protein 68-72% other wise during the Interphase – DNA Become increase 33-40%


  • Chromosome are formed by the multiple coiling of DNA
  • The DNA which is present in the chromosome are control the all metabolic activity and genetic activity.
  • In eukaryotic cell two types of DNA are present
  • 1- Normal/Unique /Non Repetitive DNA
  • 2- Repetitive DNA
  • This is present in alternative sequence.
  • In eukaryotic cell 30-35 % DNA are unique DNA.
  • In Unique DNA the Base are different to each other.
  • This DNA formed Gene which is called Exon / Cistron.
  • In Repetitive DNA Base sequence are repeated many time.
  • It formed Heterochromatic part.
  • These are called Intron


  • 5% RNA is present in Chromosome
  • It is called Chromosomal RNA
  • It help in binding of Protein to the DNA
  • It form chromatin fiber.


Two types of proteins are present in chromosome.

1- Histone protein

  • It is basic protein which made up of Arginine and Lysine
  • It is 80% part of the total protein
  • It is present in ratio of DNA : Histone = 1:1
  • It is H1, H2a, H2b, H3, and H4 types
  • It is bind to the major groove of the DNA
  • In this the positive end histone are bind to the negatively charged end of phosphate in DNA by electrostatic bond, it give DNA flexibility and stability. 

2- Non – Histone protein

  • It is 20% part of the total protein
  • It is helpful in gene regulation.
  • It do Histone DNA binding with the help of RNA.

3- Ca-Mg-Zn

They made ionic bond

And help in gene regulation

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