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
D-glucose differs from D-galactose only in the arrangement around carbon 4. Therefore D-glucose and D-galactose are- Select one: a. enantiomers b. epimers c. mirror ima

Describe Class Holothuroidea in details? Members of this Class resemble soft and squishy cucumbers lying on their sides on the bottom of the sea. On first glance, they appear n

What is Brown Algae ? Phaeophyta are commonly known as brown algae; precisely because they are - guess what? - brown in color! They are brown because they contain brown colored

What is Sporocyst? Specify. A stage in the life cycle of trematode flukes. Sporocyst develops from the mericidium found in intermediate host. Every sporocyst contains the germ


Q. What is coronary disease? The Coronary disease, or the coronary insufficiency, is a disease in which there is total or partial obstruction of one or more of the arteries tha

comparitive chart on different types of respiration obserbed in different type of respiration organ of respiration , types of respiration,energy obtained , by product formed

why psi g is ignored in water potential of plants?

How many pints (473 ml) of Fat Tire amber ale can an 80 kg person drink in Arizona before reaching the blood alcohol limit? Fat Tire's ethanol concentration of 5.3% (v/v). Assume c

List the four phases of meiosis I, and briefly explain what occurs during each phase Prophase I: DNA coils into chromosomes, the nucleolus and nuclear envelope disappear, the m