Molecular Biology & Cytogenetics

1. K.G. ART’S & SCIENCE COLLEGE RAIGARH (C.G.)
Session - 2019-20
Deparment of Zoology & Research Center
Subject :- Molecular Biology and Cytogenetics.
Seminar topic:- Chromosome.
Guided by Submitted by
Proff. Ranjana Sahu mam. Girja Prasad Patel
M.Sc. II Sem. Zoology

2. CHROMOSOME
SYNOPSIS :-
1. Introduction.
2. Definition.
3. History of Chromosome.
4. Morphology of Chromosome.
5. Prokaryotic & Eukaryotic Chromosome.
6. Structure of Chromosome.
7. Region of Chromosome.
8. Types of Chromosome.
9. Composition of Chromosome.
10.Model of Chromosome.
11.Giant Chromosome.
12.Function of Chromosome.
13.Conclusion.
14.Reference.

3. 1. INTRODUCTION :-
• “Chromosome” is a combination of two words i.e. Greek “Chroma”
= colour and “Soma”= body.
• A Chromosome is thread-like, self-replicating genetic structure is
called “Chromosome”.
• It made up of proteins and a molecule of DNA (Deoxyriboribo
nucleic acid).
• It is located inside the nucleus.
• Only visible during Cell division.
• Chromosome are seen during metaphase stage of mitosis when
the cells are stained with suitable dye and viewed under light
microscope.
• Chromosomes are the vehicle of heridity means they are passed on
from parents to offspring.

6. 2. DEFINITION :-
Chromosome is the main part of the living
cells which control all activity and heridity function of cell that are
called Chromosome .
3. HISTORY OF CHROMOSOME :-
• W. Hofmeister (1848)
First discovered chromosome in the dividing pollen mother cells.
• Strasburger (1875)
First observed chromosome during cell division.
• Waldeyer (1888)
The term chromosome however was first used.

7. 4. MORPHOLOGY OF CHROMOSOME :-
• Mitotic metaphase is the most suitable stage for studies on
chromosome morphology.
• The number of chromosomes varies from species to species.
• Generally the chromosomes are arranged in pairs. A pair of
similar chromosome is called homologous Chromosome.
• The size of chromosomes range 0.1 micron to 30 microns
• The diameter varies from 0.2micron to 2 micron in general plant
have larger chromosome than animals.
• The length of the human Chromosome from 4 micron to 6 microns.

8. SHAPE OF CHROMOSOME :-
• The shape of the chromosomes is changeable from
phase to phase in continuous process of the cell growth
and cell division.
• Chromosome contain clear zone, known as
“Centromere” or “Kinetochore” along their length.
• Centromere divide’s the chromosome into two parts, each
part is called “Chromosome arm”.
• The position of centromere varies from chromosome to
chromosome and it provides different shapes to the
chromosome.

10. Number - chromosome in every species of plant and animal, the
number of chromosome is fixed or definit in the somatic cell of one
species of animal.
• The number of chromosome and number of haploid chromosome in
their gametes (ova, sperm) will be the same. But their number varies
in the animal of different species.

12. 5. PROKARYOTIC & EUKARYOTIC CHROMOSOME :-
PROKARYOTIC CHROMOSOME :-
• Found in cytoplasm.
• Circular chromosome.
• Single chromosome + plasmid.
• Made up of only DNA.
• Copies it’s chromosomes
and divideds immediately.

13. EUKARYOTIC CHROMOSOME :-
• Found in nucleus.
• Linear chromosomes.
• Many chromosome usually
10-50 chromosome in somatic cells.
• Made up DNA, Histone proteins.
• Copies it’s chromosome grows cell
and then divides equally through
mitosis.

15. 6. STRUCTURE OF CHROMOSOME :-
• The detail structure of chromosome varies from cell to cell major
changes are associated with cell division.
• It is a prominent structure during prophase of cell division.
• Each chromosome contains one DNA Molecule. The DNA is coiled
tightly around proteins called Histone. These protein structural support
to a Chromosomes and allow the very long DNA molecule to form a
compact shape and fit inside the nucleus of a cell.
A.) Pellicle & Matrix :-
• Each chromosome is bounded by a membrane called “Pellicle”. It is
very thin and is formed of achromatic substance.
• This membrane encloses a jelly like substance which is usually called
Matrix. In the matrix is present the chromonemata. The matrix is also
formed of achromatic or nongenic material.

17. B.) Chromonemata :- with in the matrix of each chromosome are found
embedded two identical spirally coiled threads the Chromonemata or
chromonemated fibrils. Both Chromonemata are so tightly coiled that they appear
as a single thread of about 800 A° thickness..
C.) Chromomere :- during interphase , some bead like structure are found along
the length of the chromosomes which are called Chromomere. These are actually
accumulated chromatin material and tightly folded regions of DNA.
D.) Centromere :-
• Centromere is the chromosomal region that hold sister chromatid together.
• The Centromere contain complex system of fibers called kinatochore.
• Each centromere contain two kinatochore lined with chromosomal arms.
• Also termed as primary constriction .
• Darkly stained region.

18. • In humans the centromere contains 1-10 million base pair of DNA.
• Kinetochore are made up of protein fiber and microtibules which
asist in the formation of spindle during mitosis and meiosis.
E.) Arm’s:-
• Each chromosome has two arms labeled “p” (the shorter of the two)
and “q” (the longer arm).
• The “p” arm is named for “pelit” meaning “short”. The “q” arm is
named to French word “queue” meaning “tail”.
• Two arm divided at centromere. They can be connected in either
metacentric,sub-metacentric, acrocemtric, telocentric manner.
F.) Constriction :-
• A typical chromosome has narrow region called “Constriction”.
• They are two types of constriction namely – primary constriction and
secondary constriction.

19. • Primary constriction :- is made of centromere and kinetochore . The
shape of the chromosomes is determined by the primary constriction
situated at the meeting point of the arms of the chromosomes.
• Secondary constriction :- is a darkly stained constricted area. It is
associated with the formation of nucleolus. So they are refer as
“nucleolar organizer” .
G.) Satellite region :-
• The part of the chromosome which is present beyond the secondary
constriction is called “satellite region” or “trabant”.
• The varies in size according to the position of the secondary
constriction.
• If secondary constriction is very close to an end of the chromosome
the satellite may be a baiely perceptible dot.
• The chromosome having satellite is called “Sat Chromosome”.

21. H.) Telomere :-
• Derived from the greek nouns “telos” = end and “meros” = part.
• The ends of a chromosome are called “Telomere”.
• They play critical roles in chromosome replication and maintainance
of chromosomal length.
• The telomere are highly stable and telomere of different
chromosomes do not fuse .
7. REGION OF CHROMOSOME :-
(1.) HETEROCHROMATIN :-
• Darkly stained due to which it is called “Heterochromatin”.
• At that region chromatin fold it self forming a highly condensed
structure.
• Largely transcriptionally inactive preventing gene expression due
to its tightly packing.

23. (2.) EUCHROMATIN :-
• Lightly stained as they are loosely packed regions.
• It is transcriptionally active allowing expression.
• 92% of human genome consists of euchromatin.
8. TYPES OF CHROMOSOME :-
A.) AUTOSOME & ALLOSOME OR SEX CHROMOSOME :-
AUTOSOME :-
• These are present in all cells of all organism.
• Autosome that are the same size (structure) are called homologous.
• In human there are 22 pairs of chromosome.
ALLOSOME OR SEX CHROMOSOME :-
• Chromosome that are connected with the determination of sex are
called sex chromosome.

24. • Allosome are non-homologous.
• There are two types of sex chromosome ‘X’ and ‘Y’.
• ‘X’-chromosome is found in both male and female.
• ‘Y’-chromosome is found in only male.
• In human last one pair (23rd pair) of chromosome is sex
chromosome.

25. B.) BASED ON THE POSITION OF THE CENTROMERE :-
1.) Metecentric :- these chromosome are V-shaped.
they have arms equal in length having cemtromere in the center.
Exa. Human chromosome 1&3.
2.) Sub-Metacentric :- these chromosome are L-shaped.
they have arms unequal in length.
Exa. Human chromosome 4-12.
3.) Acrocentric :- the chromosome are J-shaped.
these is rod-like chromosome.
having a very small arm and a very long arm.
having centromere severaly offset from center leading.
Exa. Human chromosome 13,15,21,22.

26. 4.) Telocentric :- the chromosome are I-shaped.
having centromere at very end of chromosome.
human don’t have this type of chromosome but found in other
species like mice.

27. C.) BASED ON THE NUMBER OF CENTROMERE :-
1.) Acentric :- without centromere.
2.) Monocentric :- with one centromere.
3.) Dicemtric :- with two centromere. Eg. Wheat, Maize .
4.) Polycentric :- with more then one centromere. Eg. Ascaris,
Luzula .

28. 9. COMPOSITION OF CHROMOSOME :-
Chemical Composition :-
I.) DNA – 40%
II.) RNA – 1.5%(helps in synthesis of chromosomal fibers).
III.) Histone (Protein) – 50%
IV.) Non-Histone (Protein) – 8.5%
V.) Some amount of calcium which is attached with DNA. DNA is the
chief and most significant part of the chromosome.
DNA :- a.) Nitrogenous Base :- purine & pyrimidine.
b.) Pentose suger .
c.) Phosohate group.
Protein :- a.)Histone protein.
b.) Non- Histone protein :- Tubulin- alpha & beta, Myosine

30. a.) Histone protein :-
• Histone are the basic proteins (positively charge) in lysine and
arginine amino acids.
• Histone are highly alkalins proteins found in Eukaryotic cell nuclei
that package and order the DNA into structural units called
nucleosome.
• The histones are classified on the bases of structural differences,
Molecular weight and lysine /arginine ratio.
• All amino acid of the histone protein are in direct contact with the
DNA (negatively charged due to presence of phosphate group) or
other histone.
• The five classes of histones are H1/H5, H2A, H2B, H3, and H4.
• Histones H2A, H2B, H3 and H4 are known as the core histones.
While histones H1/H5 are known as the linker histones.
• H1, H2A & H2B are rich in lysine whereas H3 & H4 are arginine rich.

31. • Histone octamer has a structural core of an H3, H4 tetramer
associated with two H2A, H2B dimers.

32. 10. MODEL OF CHROMOSOME :-
FOLDED FIBER MODEL OF CHROMOSOME :- Folded fiber model of
chromosome structure was proposed by Du praw (1966).He published this model
based on his studies human chromosome using electron microscope. The
important features of Folded fiber model of chromosome are :
• Each chromosome contains a single but long and coiled chromatin fiber.
• this single chromatin fiber is more or less uniform in thickness.
• He suggested the cromatin fibre contents a single DNA double helix with
associated proteins
• The 20angestron thick DNA double helix is packed spirally to form a fiber.
• This fiber is then coiled to form a 10 to 100 Angestron fibers called type A fiber.

34. • Type A fiber further coiled to form 200 to 250 Angestron thick type B fiber
with a folding Ratio of 10:1.
• The 200 to 250 Angestron type B Fiber is further folded is supposed to
contain DNA histone helix. This fiber is supposed to contain DNA histone
helix
• This DNA histone helix is in a super coiled condition.
• The histone protein bound on outer side of DNA and form a shell around
the DNA.
• Du praw called this histone coat of chromosome as the “histone shell”.
• Du praw model was replaced by the most popular and universally accepted
Nucloeosome Model of chromosome.

35. NUCLEOSOME MODEL :-
• Nucleosome is the lowest level of chromosome organization in eukaryotic cells.
• Nucleosome model is a scientific model which explains the organization of DNA
and associated proteins in the chromosomes.
• Nucleosome model also explains the exact mechanism of the folding of DNA in
the nucleus.
• It is the most accepted model of chromatin organization.
• Nucleosome model of chromosome is proposed by Roger Kornberg (son of
Arthur Kornberg) in 1974.
DNA in Eukaryotes are Associated with Histone Proteins:
• The chromosomes of eukaryotic organisms composed of DNA and
associated proteins.
• The DNA and associated proteins are together called as the Chromatin.
• The protein components of chromosome (proteins interact with
DNA) are grouped into two categories.
(1). Histone proteins
(2). Non-histone proteins

37. • Histones are basic proteins (positively charged) which contain very
large amount of basic amino acids such as lysine and arginine.
• Lysine and arginine are basic amino acids since their side chain (R
group) contains additional amino (NH2) groups which can accept
protons to form NH3
+.
• There are five classes of histone proteins in the cells of eukaryotes.
• The classification of histones is based on their structural differences,
molecular weight and lysine/arginine ratio.
• The five classes of histones are H1, H2A, H2B, H3 and H4.
• The amino acid sequence of histone proteins are highly conserved
among organisms.
• The reason for this high conserved nature of histone is that, in all
organisms the histones are associated with the genetic material, the
DNA, which is identical in all the groups.

39. • Nearly all amino acids of the histone protein are in direct contact with the
DNA and engaged in interaction with DNA or other histones.
Interaction of Histones and DNA in Chromatin :-
• Roger Kornberg proposed that DNA and histones were organized into
repeated units called nucleosome.
• Nucleosome model is the most accepted model of chromatin.
• Nucleosomes are the fundamental repeating units of chromatin.
• Nucleosome represents the ‘beads’ as proposed in the ‘beads on string’
organization of chromatin.
• Each nucleosome contains a nucleosome core particle.
• The nucleosome core composed of a disc shaped structure of eight histone
proteins.
• The nucleosome core composed of two molecules of each of the four
histones H2A, H2B, H3 and H4 and his structure is called the histone
octamer.

41. • The DNA helix is wrapped as super helical left handed turn around
this histone octamer core.
• Each histone core is encircled by 1.8 turns of DNA.
• This 1.8 turn of DNA represents about 146 base pairs.
• Each nucleosome is about 10 nm in diameter.
• The H1 histone stays outside the histone octamer.
• Adjacent nucleosomes are connected by a short stretch of DNA called
linker DNA.
• Linker DNA is about 10 to 80 bp in length.
• H1 histones bind to the liner DNA.
• H1 histone binds near the site where DNA enters and exits the
nucleosome.
• The interaction of histones and DNA in nucleosome is stabilized by
several types of non-covalent bonds.

43. • Among these bonds, the ionic bonds formed between the negatively
charged phosphate groups in the DNA with the positively charged
amino groups of histones were very important.
• DNA in the chromatin attain a packing ratio of about 7:1 (seven fold
packing) by the formation of nucleosomes.
• Nucleosome units organized into more compact structure of 30 nm
in diameter called 30 nm fibers.
• The H1 histone plays very important role in the formation of the 30-
nm fiber.
• The formation of 30 nm fiber shortens genetic material (DNA)
another seven-fold.
• The linker DNA regions in 30-nm structure are variably bent and
twisted to attain the folding pattern.
• This 30 nm fibres are further folded to form the metaphase
chromosome during cell division.

46. 11. GIANT CHROMOSOME :-
I.) Polytene Chromosome :
• These are also called giant chromosome but relatively smaller than
lambrush chromosome.
• Found nuclei of the Salivery gland cells of the larvae of dipterans.
(like Drossofila have usually long and wide chromosome.)
• 100 or 200 times in size of the chromosome in other body cell of the
organism.
• The enormous size is due to the duplication of Chromonema which
do no separate.
• They are discovered by “Balbiani” (1881) and named “Koller”.
• Function :- Highly condansed of DNA so that highly transcriptionally
active because highly protein require for development.

47. • Structural Properties :-
• These are multi stranded or polytenic chromosome and may be formed of
as many as 512 to 1024 chromatid. It is due to a process called endo-mitosis
or polytenization in which there is repeated duplication of chromosomata
but not followed by their separation. So called polytenic chromosome.
• Centromere of all the chromosome and their heterochromatic region are
fused to form a darkly stained chromocenter.
• Each chromosome is with a specific pattern of dark colored bound and
alternatively arranged light coloured interband. Each dark band is
chemically formed of large amount of DNA, a small amount of RNA and
basic protein so is darkly – stained.

49. •Puffs and Balbianirings :-
• During their initial stage of development these band or interband of the
chromosome exhibit swelling or puff. Their appearance depends on the
stage of larval development, it is probable that the metabolic activity
required for the formation of puff. Are related to the secretary function of
the salivary gland. The formation of this is controlled by certain specific
genes and the puff are related with the active synthesis of RNA and protein.
This chemical composition some regions show larger puffs than others,
these larger puffing regions are called Balbiani ring.
• These rings are farmed by the lateral stretching of loop caused by
chromonemata, these loop of chromonemata make up balbiani rings and
give the chromosome a fuzzy out look.

51. II.) Lambrush Chromosome :-
• These are the largest chromosome found in the Diplotene stage of
Mitotic Prophase (I) of Amphibians Oocyte (Fishes, reptile & Birds).
• They can be seen with nached eye.
• These loops give it a brush-like appearance that is why these are
called “Lambrush chromosome”.
• Discovered by “ Ruckert” in 1892.
• Function :- I. Synthesis of RNA.
II. Formation of yolk material.

52. • STRUCTURE :-–
Chromosomal axis : each chromosome of the pair of Homologus
chromosome consists of two Chromatid, which are represented by axial
filaments. Thus the pair of Homologus chromosome has four filament in all,
the axial filaments.
• The Chromomeres consists of DNA. The loops represent lateral extensions
of the axial filaments are small swelling without loops, these are the
telomere each bivalent also contains a region called the centomere.
• Loops : loops are of two main types, typical and special most of the loops
are typical, each typical loop consists of a central axis from which are given
off RNA fibrils of progressively increasing length. This makes the loop
markedly thicker on one side, the special loop have a marked asymmetry
and have granules at the end of fibrils.

54. 12. FUNCTION OF CHROMOSOME :- they have following
functions :-
1. Genetic code storage :- contains genetic material by organism to
develop and grow in the form of gene.
2. Sex determination :- help in determining sex like in human XX-
chromosome determine female while XY determine male.
3. Control of cell division :- the chromosome of parent cell insure that
correct information and number is passed on a daughter cells during
mitosis.
4. Formation of protein & storage :- Chromosome direct protein
formed in our body and also stored in the chromosomes in the form
of histone protein that help in proper packaging of DNA.
5. Crossing over and aberrations of chromosomes introduce variations
in population.
6. They transmit heredity information from generation to generation.

55. 13. CONCLUSION :- The chromosome of a cell are in the nucleus.
Their number is fixed and definite. This is carry the genetic
information generation to generation because called heridity
vehicle.
14. REFERENCE :-
• Principles of Genetics :- D. Peter snustad & Michael J. Simmons.
• Molecular Biology of The Gene :- Watson, Baker, Bell, Gann, Levine Losick.
• Genetics :- P. K. GUPTA.
• The cell :- Albert Bruss..
• Molecular Cell Biology :- Gerald Karp.
• By Internet.