In this lesson You will learn and be able to:
• Identify where chromosomes are found in the body
• Describe the basic structure and features of a chromosome
• How many chromosomes humans have in each body cell
Nucleus
Every eukaryotic cell has a
nucleus.
Nucleus contains all the
genetic information in
structures called
chromosomes.
Chromosomes
 Chromosomes are thread like structure made up of
supercoiled DNA
 They are located inside the nucleus.
 Chromosomes can only be seen under microscope before
the cell divide (cell division)
Chromosome structure
• Each chromosome typically
has one centromere and one
or two arms called chromatid
that project from the
centromere.
• Before cell division each
chromosome is duplicated
and both copies are joined by
a centromere, resulting in an
X-shaped structure
Matching pairs
 Most cells of the body contain
chromosomes in matching pairs
based on their size and shape..
 These pairs are called homologous
chromosomes.
homologous
chromosomes
Homologous chromosomes
Where do homologous chromosomes come from?
Each pair of homologous chromosomes contains one
chromosome that has been inherited from each parent.
One chromosome comes from mother and one from father.
These two chromosomes are same in size and shape.
chromosome from
female parent
chromosome from
male parent
homologous
chromosomes
Human chromosomes
In human body cells there are a total
of 46 chromosomes.
Instead of total chromosome we
use pairs of chromosomes.
Human have 23 pairs of
chromosomes
Because You inherit half your chromosomes from
your mother and half from your father.
How many chromosomes do you inherit from each parent?
23 unpaired chromosomes
Other species
 Chromosome number is not an indication of the
complexity of a species.
Chromosomes in Humans
 A Karyotype is the full complement of chromosomes in a
particular species.
 Humans have 22 pairs of homologous (matched) autosomes
 We also have one pair of non-homologous (unmatched) sex
chromosomes
Sex chromosomes
There are two types of sex chromosome with names
that are very easy to remember!
X chromosome
Y chromosome
Females have two X (XX)
chromosomes, one from each parent.
Males have one X chromosome
and one Y chromosome (XY).
Baby boy inherit its Y chromosome
from his Father
XX
XY
Human Chromosomes: 23 Pairs
• 22 Autosomes and
one pair of sex
1
chromosome(23rd)
• The sex chromosomes
6
are different in size.
• Y chromosome is
much shorter than X
11
chromosome.
16
2
3
4
5
7
8
9
10
12
13
14
15
17
18
21
19
22
20
23
XY
In Summary
 Humans have 23 pairs of chromosomes (total 46 Chromosomes)
 Out of these 22 pairs (44) are homologous (autosomes) chromosomes
that determine all body characters.
 Only one pair of chromosome (2) called sex chromosomes are different
in males and females.
 The sex chromosome pair in females is XX means they have two X
chromosomes.
 The sex chromosome pair in males is XY means thy have one X and one
Y chromosome
 It is the male from where Y chromosome comes and therefore
determine the sex of the children.