Differentiation in somatic cells
The body organs are formed from a variety of
these tissues.
During cell division the nucleus of a somatic
cell divides by mitosis to maintain the diploid
chromosome number.
Diploid cells have 23 pairs of homologous
chromosomes.
 What is mitosis and how does it happen
again?
Diploid – containing 2 set of chromosomes (1 from each parent) (2n)
Bell Work – Put these statements in order to create a
flow chart of mitosis in your books
Two new nuclei form
Chromosomes are pulled apart
Chromosomes become visible
Chromosomes line up along the
centre of the cell
The cytoplasm splits in two
DNA and other organelles replicate
Chromosomes are not visible
Two identical daughter cells are
produced which are also identical to
the parent cell
Chromosomes are not visible
DNA and other organelles replicate
Chromosomes become visible
Chromosomes line up along the
centre of the cell
Chromosomes are pulled apart
Two new nuclei form
The cytoplasm splits in two
Two identical daughter cells are
produced which are also identical to
the parent cell
• Recall the stages of mitosis
• describe gametes as the scientific word for sex cells (sperm
and eggs)
• recall that meiosis is a type of cell division that produces
gametes
• understand why it is important that meiosis produces cells
with only half the number of chromosomes of the original
(parent) cell
• Compare and contrast mitosis and meiosis
Every cell in the
body is produced
by mitosis….
…with the exception of two types of
cells.......
What do you think these cells
are?
Why?
23
23
46
Meiosis occurs ....
• Only occurs in gametogenic areas..
• Males seminiferous tubules of testes
• Females follicles in ovaries
2n
Haploid –
containing 1 set
of chromosomes
(n) (half somatic
cell)
n
n
n
n
Why are brothers and
sisters not identical?
Or sisters and sisters
Or brothers and brothers
So how does meiosis happen?
Put these in the correct order ....
ANSWERS
The stages of meiosis are;
1) The chromosomes in the cell are
copied (same as in mitosis).
2) All the homologous (the same
type) chromosomes pair up.
Cross over occurs
3) One from each pair move to
opposite sides of the cell leading
to 2 daughter cells being
produced. These are diploid cells
containing 23 pairs of
chromosomes.
4) Each daughter cell then divides
again to form 4 other daughter
cells. These are the sex cells.
They are haploid cells containing
just 23 chromosomes.
Meiosis
1. What affect does the relative
sizes of the male and female
gametes on behaviour of
individuals?
2. What is the difference
between a haploid and a
diploid cell?
3. Why is the egg cell bigger?
4. Why is in-breeding so
harmful?
5. Since this is sexual
reproduction, what is asexual
reproduction?
Mitosis
How many cell
divisions?
How many
daughter cells are
produced?
What are they like
compared to the
parent cell?
What types of cells
does this process
produce?
Meiosis
Mitosis
How many cell
divisions?
How many
daughter cells are
produced?
What are they like
compared to the
parent cell?
What types of cells
does this process
produce?
Meiosis
Key Questions
1. What is the difference between a haploid and a diploid cell?
2. Since this is sexual reproduction, what is asexual
reproduction?
3. Where does meiosis happen?
Use relevent words to use each of the letters in meiosis
M E I O S I S
P
E
R
M
Which stage is this?