CHROMOSOMES - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.

1. Dr. P. Saranraj M.Sc., M.Phil., Ph.D., NET
Assistant Professor
Department of Microbiology
Sacred Heart College (Autonomous)
Tirupattur, Vellore District.
Mobile: 9994146964
E.mail: microsaranraj@gmail.com

2. CHROMOSOMES
 In the nucleus of each cell, the DNA molecule is packaged
into thread-like structures called Chromosomes.
 Chromosomes were first described by Straubberg in 1875.
 The trem Chromosomes was coined by Waldeyer in 1888.
 Each chromosome is made up of DNA tightly coiled proteins
called Histones that support its structure.
 Chromosomes are not visible in the cell’s nucleus not even
under a microscope when the cell is not dividing. However,
the DNA that makes up chromosomes becomes more tightly
packed during cell division and is then visible under a
microscope.
 Human cells have 46 Chromosomes (23 Identical pairs) (44
Autosomes and 2 Sex Chromosomes) (Autosomes are the
chromosomes which are not involved in sex determination)

3. Organisms Number of chromosomes
 Human 46
 Chimpanzee 48
 Dog 78
 Horse 64
 Chicken 78
 Goldfish 94
 Fruit fly 8
 Mosquito 6
 Nematode 11(m), 12(f)
 Round worm 2

4. Organisms Number of Chromosomes
 Onion 16
 Fungal Mold 16
 Carrot 20
 Tomato 24
 Tobacco 48
 Rice 24
 Maize 20

8. STRUCTURE OF CHROMOSOMES
Centromere – It is a part of chromosomes that
links sister chromatids. Centromere gives the
characteristic shape to the chromosomes and helps
describe the location of specific genes.
“P” arm – It is a short arm which is present in
upward.
“Q” arm - It is a long arm which is present in
downward.

9. Telomere – It is present in the tips of chromosome.
Chromatids – Two identical copies formed by the
replication of two chromosomes.
Chromatins – Chromatin is a complex of DNA and
Protein found in the eukaryotic nucleus which
packages chromosomes. The structure of the
chromatin varies significantly between different
stages of cell cycle according to the requirement of
DNA

10. TYPES OF CHROMOSOMES
Chromosomes are of four types. They
are:
1) Telocentric
2) Acrocentric
3) Sub – metacentric
4) Metacentric

11. 1.TELOCENTRIC
 In Telocentric, the Centromere is present at the end
of the Chromosome.
CENTROMERE
LONG ARM

12. 2. ACROCENTRIC
 The Centromere is almost terminal.
 It has one large and another very small arm.
LONG ARM
CENTROMERE
SHORT ARM

13. 3. SUB - METACENTRIC
 The Centromere is not at the middle position
of the chromosomes.
 The arms are unequal and it is ‘L-Shaped’ in
appearance.
CENTROMERESHORT ARM
LONG ARM

14. 4. METACENTRIC
 The Centromere is at the middle position.
 The arms are equal and it is ‘V-Shaped’ in
appearance.
TWO EQUAL ARMS
CENTROMERE