Chromosomes are thread-like structures found within cell nuclei that package DNA. They are only visible during cell division. Species have characteristic chromosome numbers that vary, with humans having 46. Chromosomes exist in rod, J, or V shapes depending on centromere position. Human chromosomes include autosomes and allosomes (X and Y sex chromosomes) and differ in centromere number and position.

1. Chromosome number, shape &
types

2.  Chromosome ( croma- color,soma- body)
 In the nucleus of each cell, the DNA molecule is tightly
packaged into thread-like structures called chromosomes
.
 Chromosomes are thread-like structures in which DNA is
tightly packaged within the nucleus.
 Discovered by strausberger in 1875 & term
chromosome coined by waldeyer 1888.
 visible under a light microscope only when the cell is
undergoing the metaphase of cell division.
 Chromosomes are vary in number,shape and size

3.  Chromosome number
• Each species has its own characteristic number of
chromosomes and varies from some species to species.
• Sexually reproducing species Somatic or body cells, which
are DIPLOID [2n] having two sets of chromosomes, one
from the mother and one from the father
• Asexually reproducing species have one set of
chromosomes that are the same in all body cells. However,
asexual species
can be either haploid or diploid
Organisms Chromosom
e no
Human 46
Chimpanzee 48
House mouse 40
Maize 20
 Concept of
1)euploidy
2)aneuploidy

4. Shape of chromosome
• The shape of chromosome usually determine by
the position of the centromere
• Chromosomes are generally exits in three
different shapes as fallow-
1) rod shape
2)“J "shaped
3)“V" shaped
Or terminal, sub-terminal
or median in positions

5. Types of chromosome
Human Chromosome type can be divided into-
1) Autosomes
2) Allosomes ( X or Y)
Chromosome types- based on centromere number
1)Acentric
2)Monocentric
3)Dicentric
4)polycentric

6. Type of chromosome
Based on position of centromere -
1) Metacentric
2) Sub-metacentric
3) Acrocentric
4)Telocentric
5) Subtelocentric
6) Holocentric