TNPSC Free Notes Biology – Chromosome

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

Chromosome

 The human body is made up of million cells.
 The nucleus of each cell contains thin thread like structures called
chromosomes.
 The term ‘chromosomes’ was first coined by Waldeyer in 1888.
 The chromosomes are the carrier of genetic material which contain the
heredity information.
 The chromosomes are highly condensed coiled chromatin fibres packed
with the DNA (Deoxyribonucleic acid) that forms the genetic material.

Structure of a Chromosome:
 The chromosomes are thin, long and thread like structures consisting of
two identical strands called sister chromatids. They are held together by the
centromere.
 Each chromatid is made up of spirally coiled thin structure called
chromonema.

 The chromonema has number of bead-like structures along its length which
are called chromomeres.
 The chromosomes are made up of DNA, RNA, chromosomal proteins
(histones and non-histones) and certain metallic ions.

A chromosome consists of the following regions
1. Primary constriction:
 The two arms of a chromosome meet at a point called primary constriction
or centromere.
 The centromere is the region where spindle fibres attach to the chromosomes
during cell division.
2. Secondary constriction:
Some chromosomes possess secondary constriction at any point of the
chromosome.
3. Telomere:
 The end of the chromosome is called telomere.
 It maintains and provides stability to the chromosomes.
4. Satellite:
 Some of the chromosomes have an elongated knob-like appendage at one
end of the chromosome known as satellite.
 The chromosomes with satellites are called as the sat-chromosomes.
Types of Chromosomes based on the position of Centromere:
Based on the position of centromere, the chromosomes are classified as
Telocentric, Acrocentric, Submetacentric and
Metacentric:
 Telocentric– The centromere is found on the proximal end. They are rod
shaped chromosomes.
 Acrocentric – The centromere is found at the one end with a short
arm and a long arm. They are also rod-shaped chromosomes.

 Submetacentric – The centromere is found near the centre of the
chromosome. Thus forming two unequal arms. They are J shaped or L
shaped chromosomes.
 Metacentric – The centromere occurs in the centre of the chromosome
and form two equal arms. They are V shaped chromosomes.

Types of Chromosomes based on function:
The eukaryotic chromosomes are classified into autosomes and allosomes.
 Autosomes:
 The chromosomes that determine the somatic (body) characters.
 Male and female have equal number of autosomes.
 Allosomes:
 The chromosomes which are responsible for determining the sex of an
individual.
 They are also called as sex chromosomes or hetero – chromosomes.
 There are two types of sex chromosomes, X and Y- chromosomes.
 Human male have one X chromosome and one Y chromosome and
human female have two X chromosomes.

Karyotype:
 Karyotype is the number, size and shape of chromosomes in the cell
nucleus of an organism.
 Ideogram is the diagrammatic representation of karyotype of a species.
 It consists of all the metaphasic chromosomes arranged in homologous
pairs according to decreasing length, thickness, position of centromere,
shape etc., with the sex chromosomes placed at the end.

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