Lampbrush Chromosome

1. Lampbrush Chromosome
Presented By :- Mr. Amit S. Olambe

2. Contents
①Giant Chromosome
②Lampbrush Chromosome
③Structure of Lampbrush
Chromosome
④Function of Lampbrush
Chromosome

3. Giant Chromosome
 Some cells at certain particular stages contain large nuclei with giant or large sized
chromosome they are known as giant chromosome.
 The Giant chromosomes are of two types; Lampbrush chromosome and Polytene
chromosome. The term giant chromosome was given by Winchester.
 Found in certain tissues e.g., salivary glands of larvae, gut epithelium, Malphigian
tubules and some fat bodies, of some Diptera (Drosophila, Sciara, Rhyncosciara)
 These chromosomes are very long and thick (upto 200 times their size during mitotic
metaphase in the case of Drosophila)

4. Lampbrush Chromosome
Lampbrush Chromosome were first observed in Salamander (Amphibians)
oocytes by Walther Flemming in 1882.
Later Ruckert (1892) described in shark oocyte & coined the term
Lampbrush.
The name Lampbrush Chromosome is derived from their resemblance to
brushes used for cleaning kerosene lamp.
Lampbrush chromosome occurs at the diplotene stage of (meiotic
prophase-1) in primary oocytes of all animals species both vertebrates and
invertebrates except mammals.
Visible under light microscope.

5. Lampbrush chromosomes are intermediate structures present during the first
meiotic division.
They are present in the form of bivalents in which the maternal & paternal
chromosomes are held together by chiasmata.
central axis consist of 2 bivalent homologous chromosome each with 2
chromatids. So, altogether there are 4 chromatids.
Each chromosome has several chromomeres distributed over its length.
From each chromomere, a pair of loops emerges in the opposite directions
vertical to the main chromosomal axis.
Usually, 1-9 loops may arise from each chromomere.

7. Lateral loop contain a fully extended DNA duplex. They are believed to
be formed by the uncoiling of the sister chromatids.
Lateral loops contain bundles of sub microscopic fibrils.
Both the central axis & the loop axis are formed of
Deoxyribonucleoprotein.
The loop axis may be coated with matrix of RNA & proteins.
The lateral loops are active site of RNA synthesis (genetic
transcription)
Each loop may contain one or more transcription units (transcriptons)
Each bivalent may contain a loop less swelling also it represents the
centromere

8. Newly synthesised RNA molecules associate with proteins & form a
ribonucleoprotein (RNP) matrix.
But some of the mRNA molecule play an active role in the subsequent
development of the zygote.
Small swelling without loops may be present towards the end of
central axis, they represent the telomeres.
Each bivalent may contain a loop less swelling also it represents the
centromere.
Lampbrush chromosomes are up to 800 um long; thus they provide
very favorable material for cytological studies.
The lampbrush chromosome loops are used to studying transcription

9. Structure of Lampbrush
Chromosome

12. Function of Lampbrush Chromosome
It is involved in the synthesis of mRNA and therefore proteins that are
needed for heavy demand of embryonic development.
 It is also involved in the production of “masked” mRNA for early
development.
 Each loop is believed to represent one long Operon consisting of
repititive citrons to meet high rate of synthesis.
Each locus codes for RNA.
It also helps in the formation of yolk material in the egg.
 It has been shown that disintegrating loop ceases the formation of
lampbrush chromosome (LBC).

13. THANK YOU