Special chromosomes are chromosomes where certain type of chromosomes present in certain type of tissue....

1. KUVEMPU UNIVERSITY
PG Department of studies and Research in Biotechnology
Sahyadri Science College, Shivamogga
Seminar Report on
“SPECIAL CHROMOSOMES.”
Under the Guidance of
Dr. C K RAMESH
Associate professor & PG Co-ordinator
Department of Biotechnology,
Sahyadri Science College, Shivamogga
Submitted By:
IMMACULATE HARSHITHA A
I MSc, I Sem
SAHYADRI SCIENCE COLLEGE
Shivamogga

2. CONTENTS:
• INTRODUCTION
• STUCTURE OF CHROMOSOME
• SHAPE OF CHROMOSOME
• FUNCTION OF CHROMOSOEM
• SPECIAL CHROMOSOME
• POLYTENE CHROMOSOME
• LAMP BRUSH CHROMOSOME
• SUPER NUMERARY CHROMOSOME
• CONCLUSION
• REFERENCE

3. SPECIAL CHROMOSOMES
INTRODUCTION:
• Nucleus is defined as any formation surrounded by cytoplasm from which chromosomes arise
during cell
division.
• It was first discovered by Robert Brown in 1831.
• The nucleous is enclosed of nuclear membrain and it contain genetic material, and it is organized as
DNA molecules, along with protein veriety of protiens,to form chromosome.
• Chromosomes are self replicating thread like structure,
• [chroma=colour, soma=body] they can easly stained with dyes. They are vehicles of heredity.
Chromosomes were first observed by Hofmeister in 1848.
• The number of chromosomes varies from species to species. But the number remains constant
among the member of same species.
• The lowest number of chromosomes is 2 and it occurs is Ascaris melanocephala. And the maximum
number of chromosome is 1700 and it occurs in Radiolarian [Protozoa]

4. STRUCTURE OF CHROMOSOME:
In eukaryotes the chromosomes are multiple large, linear and are present in the nucleus of the cell. Each
chromosome typically has one centromere and one or two arms and projects from the chromomere.
The different parts are,
• Pellicle : It is a outer envelope around the substance of chromosome
• Matrix : It is the ground substance of chromosome which contain
the chromonemata.
• Chromonemata : Embedded in matrix of each chromosome are spirally
coiled threads.

5. SHAPE OF CHROMOSOMES:
The shape of chromosome is largely determined by the position of its centromere. On this basis they are
classified into four types, They are as follows:
• Telocentric
• Acrocentric
• Submetacentric
• Metacentric
The length of the chromosomes varies from 4 microns to 6 micron. There are some special
chromosomes which are gain chromosomes that is varies in length and diameter. That is Lamp brush
chromosome and polytene chromosome thesr are special type of chromosome.

6. FUNCTION OF CHROMOSOMES:
• They control the heredity.
• The chromosomes control the metabolism of an organism.
• The heterochromatin helps in the formation of nucleolus.
• Chromosome control the differentiation of different characteristics of an organism.
• Change in the position, number and the structure of chromosome lead to the formation of new
species.

7. SPECIAL CHROMOSOMES:
WHAT IS SPECIAL CHROMOSOMES………..?
In organism certain chromosomes are found in certain special tissues and are not seen in other tissue with
different structure, size, shape and function have been found in varied groups of animal and plants. The
most important are giant chromosomes and supernumerary chromosome.
GIANT CHROMOSOME:
These are exceptionally larger chromosomes. They are described as usual chromosome by A. M.
Winchester. There are two types of chromosome namely,
• Polytene chromosome
• Lamp brush chromosome.
SUPERNUMERARY CHROMOSOME:
These are also known as B- chromosomes/ accessory, or lineage-specific chromosomes.

8. • It was discovered by Balbiani in 1881.
• It is found in the salivary gland cells of Chironomus larva. Hence it is also called salivary gland of chromosome.
• It is a giant chromosome. It is larger in size. For example, in Drosophila melanogaster it is 1000 times larger than
somatic chromosomes.
• The larger size of the chromosome is due to the presence of many longitudinal strands called chromonemata.
Hence they are also called polytene chromosomes (many strand).
• The many strands of the giant chromosome are due to repeated division of the chromosome without the cytoplasmic
division. This type of division is called endomitosis.
• The polytene chromosome contains two types of transverse bands, namely dark bands and inter bands. The dark
bands are darkly stained and the inter bands are lightly stained with nuclear stains. The dark bands contain more
DNA and less RNA. The inter bands contains more RNA and less DNA.
• The bands of polytene chromosomes become enlarged at certain times to form swelling called Puff or Balbiani rings.
The formation of puff is called puffing. In the puffs region the chromonenata uncoil and open out to form many loops.
POLYTENE CHROMOSOME:

10. Contn….
• Polytene chromosomes are usually found at the interphase nuclei of some tissue of the larvae of flies.
• Polytene chromosome are very useful for the analysis of eukaryotic interphase chromosome.
• They developed from a chromosomes of diploid nuclei by successive duplication of each chromosomal
element.
• The formation of polytene chromosome is associated with the elimination of the final steps of mitosis
after each doubling of DNA. This result in the cell cycle consist of just two phases,
1. synthetic (S)
2. Intersynthetic(G)
As a result giant chromosomes is formed, and these giant chromosomes are 70-110 times longer than
typical metaphase chromosomes.

11. Function of Polytene chromosome:
 Polytene cells may also have a metabolic advantage as multiple copies of genes permits a high level of gene
expression.
 The inter bands are involved in the interaction with the active chromatin proteins, nucleosome remodeling,
and origin recognition complexes.
 Their primary functions are: to act as binding sites for RNA pol II, to initiate replication and, to start
nucleosome remodeling of short fragments of DNA

12. Lamp brush chromosomes:
• It was discovered by Flemming in 1882.
• It contains lateral loops and appears like a brush. Hence the name lamp brush chromosome.
• It is found in the oocytes of Sagitta, Sepia, Echinaster (Echinoderm), insects, sharks, amphibians, reptiles and birds.
• It is a giant chromosome, and it is larger in size,
• Each lamp brush chromosome consists of a main axis and many lateral loops.
• The main axis of each chromosome is formed of 4 chromatids.
• From each chromomere a pair of lateral loops open on each side.
• Each loop has an axial fiber. It contains DNA
• The axile fiber of the loop is surrounded by a matrix. The matrix is formed of RNA and protiens .
The matrix gives a fuzzy appearance.
• The synthesis of proteins and yolk takes place in the lateral loops.
• LBCs’ length ranges (depending on the species) from 400 to 800 mm, which makes them up to 30times larger
than their normal mitotic counterparts.
• The are generally smaller in invertebrates than vertebrates.

14. Contn…….
• The opposite loops are always symmetrical.
• Each chromosome in the bivalent.
• However, the centromeres of each of the chromosomes do not have loops. There are around 10000 loops per
chromosome.
• The lateral loops contain 5 to 10 % of DNA.
• The length of the loop is 10 micro metre and its diameter is around 1 micro metre.
• The Loops are rich in RNA.

15. FUNCTION OF LAMP BRUSH CHROMOSOME:
• Its major function of Lamp brush chromosome is to help in RNA synthesis and lipid or yolk synthes.
• Complex loops are classified as marker loops that enable chromosome identification or side loops.
• Each lateral loop contains one or several transcription units with polarized RNA-matrix coating the DNA axis of the
loop. And also in loop gene amplification takes place.

16. SUPER NUMERARY CHROMOSOMES:
The supernumerary chromosome is also known as accessor chromosome, B-chromosome, Some plants and animal
nuclei, possess one or more extra chromosomes, in addition to normal chromosomes. They are called supernumerary
chromosomes.
These are first discovered by Wilson(1905) in Hemipteran insect, Metapodius terminals. They are smaller in size and
genetically inert
The distinction between A-chromosome(the normal chromosome) and the B-chromosome was made by the Randolph
(1928), and it is with his well known researches on the B-chromosomes of maize.

17. CONCLUSION:
Chromosomes are found in the nucleus of the cell. Which is in tread like appearance called chromatin fibers. These
chromatin fibers are condensed to form a chromosome.
In eukaryotic organism certain chromosomes are found only in certain special tissues and are not seen in other tissues.
These chromosomes are larger in size and are called giant chromosomes. These are two type of giant chromosomes i.e
polytene chromosome and lamp brush chromosome. Where it is due to the repetitive chromosomal division and
elimination of cytoplasmic division which leads to the formation of giant chromosome.

18. REFERENCES:
 Mohan P Arora & Gurdarshan S. Sandhu, (2012) Genetics, sixth revised and enlarged edition.
By Himalaya publishing house.
 P.S Verma & V.K Agarwal,Genetics, first multicolour edition. By S Chand and company limited, New Delhi.
 Dr Ajoy Paul, Text book of Genetics- from Genes to Genomes. By Book and allied (P) Ltd. Kolkata.
 https://www.biologydiscussion.com/chromosomes/special-type-of-chromosomes-with-diagram/36863
 http://images.app.goo.gl/pDPFXHxR7zwEWvbV6