Chromosomes contain DNA organized with proteins. During cell division, chromosomes condense into thick, distinct structures that can be seen. They contain genes that control characteristics. In humans, body cells have 46 chromosomes while sex cells have 23. Chromosomes differ in size, centromere location, arm length, and shape during cell division. They are made up of telomeres, chromatids, centromeres, and primary/secondary constrictions. The DNA is tightly packed with histone proteins to regulate gene expression and fit inside cells.

1. Morphology of
chromosomes

2. ⦿ Nucleoplasm contain chromosomes.The
DNA is organized with protein to form
chromosomes.The chromosomes is
thread like structure during interface so
they are not identified as an individual
structure.Thus a chromosome appear as
a mass of sustained material.This sustain
material is known as chromatin.

3. ⦿ The chromosome condense before the
division of cell so it become thick and
can be seen as a separate structure.
Chromosome contain genes.These genes
control all the character e.g. human have
46 chromosome in the nucleus
but sex cell such as egg and sperm have
only 23 chromosome in human

4. ⦿ The chromosome is widely differ
in appearance they are vary in
size due to
1. staining properties
2. location of centromere
3. relative length of two arms
4.position of arms

5. ⦿ Chromosomes have different shape at the
time of anaphase during cell division
⦿ Three types
i, j, v shape

6. Chromosome is made up of four
different things
⦿ Telomere
⦿ Chromatids
⦿ Centromere
⦿ Primary and secondary constriction

7. Telomere
1. It is present at each end of chromosome.
2. It also bind with specific proteins and these
proteins protect chromosome from attack
(of other chromosome/cells)
3. It also involved in attachment of
chromosomes ends nuclear membrane and
permit DNA replication.
4. It also involved in U-shaped pairing of
homologous chromosomes during meiosis.
5. The structure of telomeric DNA is very
similar in all eukaryotic organism.

8. Chromatids;
⦿ Each chromosome contain 2 chromatids.
⦿ Both the chromatids are exact copy of
each other and held together by
centromere.
⦿ Both chromatids separate from each
other during anaphase.

9. Centromere;
1. The chromatids of each pair of
homologous chromosomes are held
together at centromere.
2. It is responsible for proper segregation
of each chromosome pair during cell
division
3. It contain DNA which is called
heterochromatin.

10. Primary and secondary
constriction;
⦿ Each chromosome has special
constriction at two points.
⦿ 1st
present at the site of centromere. It is
called primary constriction.
⦿ One or more pair of chromosome in each
species have also 2ndry constriction. It
does not stain well. Nucleolus is attached
with this region then this region contain
multiple copies of genes that transcribe
ribosomal-RNA within the nucleolus.

11. Types of chromosomes;
1) Telocentric
2) Aerocentric
3) Submetacentric
4) Metacentric

12. 1) Telocentric
⦿ Rod like chromosome centromere is
present at the end of chromatids.

13. 2) Aerocentric;
⦿ Centriole is present near the end of
chromatids.The chromosome have 2 very
small, 2 very large arm.

14. 3) Sub metacentric;
⦿ Centriole is present near the middle of
the chromatids. Chromosomes contain
arms of unequal length.

15. 4) Metacentric
⦿ Centromere is present at the middle of
chromatids. Chromosome contain equal
arms.

16. Ultra structure of
Chromosome;
⦿ Chromatin consist of DNA and histone
protein.This association of DNA and
protein help in the complex packing of
DNA into chromosome so it regulate the
DNA activity.
⦿ These are five different types of histone
protein
⦿ H1
⦿ FBA
⦿ H2B
⦿ H4

17. ⦿ ULTRA STRUCTURE IN
DIFFERENTWAYS

18. Nucleosome;
⦿ Four type of histone protein form a core
particle is called nucleosome.
⦿ It is composed of 8 molecule of histone
⦿ Histone have high proportion of +ively
charged amino acid so they bind tightly to
the –ively charge of DNA and form
chromatin.
⦿ The DNA coil around the nucleosome .
Chromatin organization control the
transcription of DNA therefore nucleosome
expose gene expression.

19. Linker protein;
⦿ The histone protein H1 is
called linker protein.
⦿ It is not needed to form a
nucleosome but it fixed
DNA with nucleosome.