Structure of chromosome, Biology

STRUCTURE

  • 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

ROBERT SOVIAN CHANGE

  • 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
Explain about the Niacin (nicotinic acid) deficiency? Niacin (nicotinic acid) deficiency classically results in pellagva, which is a chronic wasting disease associated with a c

The normal flow pattern cross-mitral valve is a tall E wave where is due to early rapid filling and small A-wave which is due to atrial contraction. E/A ratio >1. Pulmonary

Q. What are the major components of the cytoskeleton? The cytoskeleton is a network of very small filaments and tubules distributed throughout the cytoplasm of eukaryotic cells

Discuss blood types, the factors in crime scenes. What is a criminal case where blood samples were important in the case decision and outcome, what was it about the blood in this c

Q. Which other phylum of the animal kingdom present species with exoskeleton? Arthropods present exoskeleton made of chitin. Echinoderms do not have exoskeleton but they presen


distinguishing characteristics of phylum platyhelminthes?

Unlike the phagocytosis, that is a regulated form of endocytosis carried out by a small number of cell category, pinocytosis is a constitutive process which happens continuously in

Explain the Composition of Nutrient Agar and Nutrient Broth? The composition and procedure for preparation of some commonly used media, which we will use in the laboratory for

Define Protein Requirement at Different Stages of Life Cycle? Methods of Estimating and Assessing Protein Requirements at Different Stages of Life Cycle In this section, we