MOLECULAR
STRUCTURE OF
CHROMOSOME
MA D E BY: A N O O D S H A R I Q
S U B M I T T E D T O : D R . I S R A R A H MA D
S U B J E C T: G E N E T I C S
C O U R S E : M. S C . . B I O T E C H N O LO GY 2 N D
S E M E S T E R
W H AT I S A C H R O M O S O M E ?
• A chromosome is a thread like self-replicating genetic structure containing
organized DNA molecule present in the nucleus of the cell
• Chromosomes can be seen under the light microscope at the metaphase
stage of mitosis.
• E. Strasburger discovered thread like structures in 1875
• In eukaryotes, each species have a definite number of chromosomes as well
as definite size and shape.
C O N T I N U AT I O N
• Waldeyer coined the term chromosome in 1888
• Somatic cells have diploid chromosome number (2n)
• Game cells have haploid number of chromosome (n)
• When 2 copies of chromosomes are identical in morphology, gene content
and gene order, they are homologous.
• 2 types of chromosomes;
• Autosomal and Allosomes
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STRUCTURE OF CHROMOSOME
• The morphology can be studied in metaphase stage.
• During cell division, the structure changes. Normally they are thin,
coiled, elastic and thread like during interphase.
• When they enter metaphase, they become highly condensed and thick.
• The general structures include, arm, centromere, telomere, etc
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T H E C H R O M AT I D
• When metaphase chromosome is longitudinally divided into 2 identical parts,
they form chromatid.
• The 2 chromatids join at the centromere.
• During anaphase, it is these chromatids that get separated in opposite poles
• Sister chromatids are formed when replication of single chromatid occurs
during s phase of interphase.
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CENTROMERE
• This is also the primary constriction
• It can be used for identification of a chromosome
• The centromere divides the chromosome into 2 arms
• The short arm of the chromosome is the 'p' arm
• The long arm of the chromosome is the 'q' arm
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TELOMERE
• These are the structures present at the two ends of the chromosome.
• They have a very important role in chromosome replication and maintenance
of chromosome length.
• They are highly stable.
• Telomeres of different chromosomes do not fuse.
• This telomeric region is made up of repetitive T and G bases
S E C O N D A RY C O N S T R I C T I O N &
S AT E L L I T E
• In some chromosomes, there is a secondary constriction also present.
• It is usually present near the telomeric end.
• The region between secondary constriction and nearest telomere is called
the satellite.
• Chromosomes having satellite are called satellite chromosomes.
SIZE OF CHROMOSOME
• At different stages of cell cycle, the size of the chromosomes vary.
• They are longest and thinnest at the interphase
• They are smallest and thickest at metaphase
• The size is not proportional to the number of genes present on chromosome
• The location of centromere gives chromosome it's shape
M E TA C E N T R I C
• The centromere is located in the center of chromosomes.
• This means that the centromere is the median.
• The centromere is present between each end and the 2 arms are equal in
length
• Metacentric chromosomes take V shape during anaphase
S U B M E TA C E N T R I C
• Centromere is located on one side of the central point of a chromosome.
• Centromere is the submediant, giving one longer and one shorter arm.
• Submetacentric chromosomes may be J shaped or L shaped during
anaphase.
ACROCENTRIC
• The centromere located close to one end of chromosomes.
• The centromere is terminally placed and forms very unequal arm length.
• The p (short) arm is so short that is hard to observe but still present.
• Acrocentric chromosomes may be rod shaped anaphase.
TELOCENTRIC CHROMOSOMES
• Centromere located at one end of chromosome lies at one end.
• Telocentric chromosome may be rod shape during anaphase
• According to the number of centromere the eukaryotic chromosomes may be:
a. Acentric: Without any centromere
b. Mono centric: With one centromere
c. Dicentric: With two centromeres
d. Polycentric: with more than 2 centromeres
D N A PAC KA G I N G
• To fit the long DNA molecule inside the nucleus, we have several stages of
DNA packaging.
• This involves the nucleosome model
• The solenoid model
• The 30 nm fiber
• Additionally, DNA binding proteins and other enzymes are also needed for
effective packaging.
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REFERENCES
• https://medlineplus.gov/genetics/understanding/basics/chromosome/#:~:text
=Each%20chromosome%20is%20made%20up,the%20cell%20is%20not%20
dividing
.
• https://byjus.com/neet/important-notes-of-biology-for-neet-chromosome-struc
ture/
• https://www.britannica.com/science/chromosome
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TTHHAANNKK YYO
OUU!!
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