in this slide Include three type of special chromosome first is giant chromosome , second is lampbrush and last one is B- chromosome.

1. Presentation topic is-
SUBMITTED TO:
DR.PRABHA RANI CHAUDHARI
DR.RAJEEV SHRIVASTAVA
DEPT-GENETICS AND PLANT BREEDING
IGKV, RAIPUR , CG
COURSE NO. GP-502
COURSE TITLE- PRINCIPLE OF CYTOGENETICS
PRESENTED BY:
ANKIT TIGGA
MSc(AG) PREVIEWS YEAR
DEPT-GENETICS AND PLANT BREEDING
IGKV,RAIPUR , CG

2. WHAT IS A SPECIAL TYPES OF
CHROMOSOME
A chromosome which is significantly differ in structure and function
from normal chromosome are known as special chromosomes such
chromosome include:
GIANT CHROMOSOME LAMPBRUSH CHROMOSOME B-CHROMOSOME

3. What is Giant chromosome
 The multiple replicates of the same
chromosome holding together in a
parallel fashion resulting in a very
long and very thick structure is
called giant chromosome .
 First discovered by Balbiani (1881) in
dipteran salivary glands of
drosophila hence are called salivary
gland chromosome.

4.  Found in certain
tissues e.g salivary
glands of Drosophila
and chironomus larva,
sciara , malphigian
tubules and fat
bodies of some
diptera etc.
OCCURRENCE
Salivary glands of
drosophila
Sciara
Chironomus larva

5.  These chromosome are very
long and thing during mitotic
metaphase in the case of
Drosophila.
 In somatic cell of drosophila
only found 4 giant
chromosome.
 The total length of D.
melanogaster giant
chromosome is about 2000
micron and length of normal
chromosome measures only
7.5 micron .
SIZE OF GIANT CHROMOSOME

6.  All the available evidence clearly
shows that each giant
chromosome is composed of
numerous strands, each strand
representing on chromatid.
 Therefor, these chromosome
are also known as” Polytene
chromosome”.
 Term polytene was given by
koller (1935)
STRUCTURE OF GIANT CHROMOSOME

7.  Giant chromosome are made
up of several dark staining
regions called band.
 In drosophila about 5000
bands can be recognized.
 It can be separated by
relatively light or non-staining
regions is called interband .
 Some of these bands are as
thick as 0.5 micron while some
may be only 0.05 micron thick.

8.  After staining polytene
chromosome show
alternate dark and light
bands all along their
length at places polytene
chromosome bear
swelling called
chromosome puffs while
the larger swelling are
called Balbiani rings.
 Puffs are site of RNA
synthesis.
 Ecdysome induces puffs
in specific band.
MAIN FEATURES OF GIANT CHROMOSOME

9.  Repeated cycles of endo-reduplication are found.
 The number of strand doubles after every round of
DNA replication . It is estimated that giant
chromosome of drosophila have 1024 strands and
chironomous may have as many as 4096 strands.
 Chromosome replicate but can’t get sepration .
 The puffing of polytene chromosome is acyclic event
and has got a definite role in moulting of insect.
 Rich in DNA content.

10. LAMPBRUSH CHROMOSOME
 Chromosome have a pair of several chromomere
distributed over its length and from each
chromomere , lateral loops extend in opposite
directon perpendicular to the main axis of
chromosome. These loops give the appearance of
lampbrush.
 1ST seen by Flemming (1882) in ambhibian oocyte.
 Detailed given by Ruckert 1892 in the oocytes of
sharks.

11.  Found in oocytes of insects, sharks ,
amphibians, frog and birds which
produce large and yolky eggs or all
vertebrates.
 They are also found in plant and some
invertebrates like sepia and echinaster.
OCCURRENCE
Echinaster
sepia

12. SIZE OF LAMPBRUSH CHROMOSOME
These chromosome are extremely long in some cases being
800 to 1000 micron in length and about 20 micron width.
Salamander oocyte they may attain a length about of 5900
micron.

13.  Lampbrush chromosome found in the form of
paired homologous chromosome joined at
places called chiasmata.
 They are found at the diplotene stage of
meiosis in the primary oocyte of all animal
species.
 Lampbrush chromosomes appears like a
brush.
 Each chromosome has along axis and lateral
loops.
 Thus the DNA axis of loops moves
progressively from the thin end toward the
thick end of loops; it about 10 days for a point
to move from the thin end to the thick end of
the loop.
Structure and features of lampbrush chromosome

14.  Loops are produced due to uncoiling of chromatin
fiber.
 These loops make their DNA available for
transcription (RNA synthesis).
 One end of each loops is thin (supports active RNA
synthesis) while other end is thicker.
 The size of loops may range from an average of 9.5
micron in frog to up to about 200 micron in
salamander.
 Form chromosome lateral loops extend.
 Each loop consists of a DNA covered by
Matrix(RNA and proteins).
 Loops are site of RNA synthesis.

15. What is a B-Chromosome
 Chromosome which are found in addition to
normal chromosome complement of a species
and are not essential for normal growth and
development. Also know as extra ,
supernumerary , and accessory chromosome .
 First reported in maize by Longley(1927) and
Randalph(1928).
 The term B-chromosome was first used by
Randalph(1928).
 This chromosome broadly similar to the normal
somatic chromosome in their morphology.

16. General properties
Differ morphologically from A chromosome.
In wild populations around 100 animal species 600 plant species
especially fungi contain B-chromosome.
Leads to some reduction in vigour and fertility in maize.
B-chromosome are largely heterochromatic.
Carry no genes with major effects.

17. 90 % of these B-chromosome tend to lack centromere. They are to
move towards either of centrioles and poles during cell division.
Smaller in size and carry less DNA than A chromosome.
Non mendelian inheritance i.e. no pairing and random distribution
during cell division .