Structure of chromosome, Biology


  • Each chromosome composed of two interwoven (coiled) threads called Chromonema (Chromonemata) embeded in a matrix of semisolid protein.
  • Surface of matrix is in form of a membrane called Pellicle.
  • Chromonema name proposed by Vejdowsky.
  • Each Chromonema is composed of a single DNA molecule.
  • Coiling of chromonema is of two types -
  • Plectonemic coiling is characteristic of Mitotic Chromosomes (Prophase) while meiotic Chromosomes in prophase stage have paranemic coiling.

577_chromosome structure.png

  • Chromomeres - Dark granules on Chromonema.
  • Chromomeres form due to extensive folding of DNA molecule.
  • Two types of constrictions occur on Chromosome -

(1) Primary constriction or Centromere :- This is specialized and essential constriction on chromosome.

(i) Centromere remains unstained (Achromatic).

(ii) Pellicle is absent on centromere.

(iii) Each chromonema is associated with a disc shaped protein called Kinetochore. Centromere is essential for division of Chromosome and its movement towards poles during anaphase. Kinetochores provide attachment site to spindle fibers. Chromosome without centromere (Acentric) may last during cell division.

(2) Secondary constriction - It is ordinary constriction and it is nonessential part of Chromosome. In chromatin, sec. constriction occurs as heterochromatin.

  • Part of Chromosome after sec. constriction is called Satellite body or Trabant.
  • Nucleolar organiser is a type of satellite body.
  • Chromosomes having satellite body are Called SAT chromosome (SAT = "Sine acid thymonucleinico" which refers to low DNA percentage)
  • Satellite body of Chromosome have repetitive genes. Le. same type of genes are present many times.
  • Nucleolar organiser is termed as sec. constriction-I and others as sec. constriction-II
  • On the basis of position of Centromere, Chromosomes are of following types -

(i) Chromosomes which do not have centromere is called "Acentric."

(ii) On the basis of number of centromere chromosomes termed as Monocentric, diacentric and polycentric.

Based on the position of centromere chromosomes are of four types -

1.       Telocentric - Centromere terminal

2.       Acrocentric - Centromere inner to telomere

3.       Submetacentric - Centromere submedian

4.       Metacentric - Centromere median

1677_chromosome structure1.png


  • If centromere of a metacentric chromosome is splitted then two telocentric chromosomes are formed such change is called Robert sovian change. It is a type of mutation.
  • If arm of a telocentric chromosome is splitted upto centromere then a metacentric chromosome with two identical arms is formed. Such Chromosome is called Isochromosome.
Posted Date: 10/8/2012 3:10:00 AM | Location : United States

Related Discussions:- Structure of chromosome, Assignment Help, Ask Question on Structure of chromosome, Get Answer, Expert's Help, Structure of chromosome Discussions

Write discussion on Structure of chromosome
Your posts are moderated
Related Questions
What is the difference between facultative anaerobic beings and obligate anaerobic beings? Facultative anaerobic beings, such as the fungi Saccharomyces cerevisiae, a brewing y

Nerves - Organisation of Nervous System Due to the pattern of distribution of neurons as described above, there are bundles of nerve fibers, called nerves, connecting the cent

Q. Describe Cluster analysis? After making a similarity table, it is then rearranged so that OTU's whose members have the highest mutual similarity are brought together. This c

Q. What is green fluorescent protein (GFP)? Green fluorescent protein is a protein which is found in a luminescent jellyfish (Aquorea victoria) that lives in cold waters of nor

habitat, habit, cell wall chemistry, reason why cell wall like this of Archaebacteria , eubacteria,fungi,algae,bryophytes ,pteridophyes, gymnosperms , angiosperms..

Explain the Bacillus - Characteristics of Bacteria? Bacillus - It is gram positive, endospore former, obligate aerobic or facultative aerobic rods belonging to order Bacilliale

What are the reasons of Food Processing? The reasons for food processing may vary, but the main objectives are to: Preserve the nutritive quality of food by preventing th

How many parts of human body?

How can we check BP without stethoscope In this case the procedure is same except you place your hand on radial pulse. You can read systolic pressure only by this method. -