Structure of chromosome, Biology

Assignment Help:

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.

Related Discussions:- Structure of chromosome

What do you mean by descending aorta, Q. What do you mean by Descending Aor...

Q. What do you mean by Descending Aorta?  The descending aorta begins at the level of the fourth thoracic vertebra. It is defined through the cardiac shadow on the CXR, as it l

Show the ph range of natural honey, Q. Show the pH range of natural honey? ...

Q. Show the pH range of natural honey? The pH of natural honey ranges from 3.4 to 6.1. Acidity of honey is primarily due to presence of acids such as gluconic acid, pyruvic a

How to removes hydrogen from fatty acids, Suppose you treated butter with a...

Suppose you treated butter with a fatty acid desaturase, an enzyme that removes hydrogen from fatty acids and creates double bonds. What would happen?

Prevention of outbreak in salmonellosis, Q. Prevention of Outbreak in salmo...

Q. Prevention of Outbreak in salmonellosis? Prevention of Outbreak: The control of food borne salmonella infection requires the following: 1. Preventing food contamination

Explain about amino acids, Do the -R groups bound to the central carbons pa...

Do the -R groups bound to the central carbons participate in the union among amino acids? The peptide bond attaches the nitrogen of the amine group of one amino acid to the car

Explain difference between sonication and homozinization, Homogenization is...

Homogenization is intensive blending of mutually related substances or groups of mutually related substances to form a constant of diverse insoluble phases (sometimes withaddition

Foot examination for an diabetics, Foot examination For all diabetics, ...

Foot examination For all diabetics, foot examination is important and necessary in all visits to identify risk factors of ulcers or injury of foot. This will help in preventing

Diet, heating a food sample with Benedict''s solution is a test for...

heating a food sample with Benedict''s solution is a test for...

Role of cell death, Role of cell death As development of the limb proc...

Role of cell death As development of the limb proceeds waves of death or necrosis of large masses of mesodermal cells occur in certain regions at different stages. This has be

What are the typical features of mammals, Q What are the typical features o...

Q What are the typical features of mammals? The typical features of mammals are: body (less or more) covered with hair; presence of the diaphragm muscle that separates the thor

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd