The process of meiosis

1. Life Sciences
Human Reproduction- Meiosis
By Ipeleng.R.Makgaka

2. What is meiosis?
• Meiosis like Mitosis is cell division
• However meiosis is the process that converts
diploid nuclei to a haploid nuclei.
• In other words meiosis takes diploid body cell
which has 46 chromosomes and converts it
into a haploid sex cell which has 23
chromosomes.

3. Where does meiosis take place?
• Meiosis takes place in the sex organs,
producing gametes.
• Gametes are sex cells: sperm or eggs.
• Gametes have to be haploid so that once
fertilization takes the haploid sperm can fuse
with haploid egg to form diploid zygote.
• Therefore a zygote has a diploid number of
chromosomes, one set from each parent

4. A Life cycle

5. Meiosis consists of...
• Meiosis consists of two
stages namely, Meiosis I
and Meiosis II
• Meiosis I consists of five
phases namely,
InterphaseI, ProphaseI,
MetaphaseI, AnaphaseI,
TelophaseI.
• Meiosis II consists of four
phases namely,
ProphaseII, MetaphaseII,
AnaphaseII, TelophaseII.

6. Meiosis I- Interphase I
• The cell builds up
energy in order for DNA
Replication to take
place.
• DNA is replicated to
make sure that
chromosomes are
duplicated.
• The cell does not
change structurally.

7. Meiosis I- Prophase I
• The chromosomes coil and
become individual
chromosomes.
• The nucleolus and Nuclear
envelope begin to disappear.
• Homologous chromosomes
come together and exchange
genetic information through
the process of crossing over.
• This will ensure genetic
variation.
• The Centrioli moves towards
opposite poles with spindle
fibres between them.

8. Meiosis I- Metaphase I
• The Centrioli has
reached the poles.
• The homologous pairs
align at the cell equator.
• The two chromosomes
attach to one spindle
fibre by means of the
centromere.

9. Meiosis I- Anaphase I
• The Spindle Fibres begin
to contract.
• This causes the
duplicated
chromosomes to move
towards opposite poles

10. Meiosis I- Telophase I
• The duplicated
chromosomes have
reached the opposite
poles.
• A nuclear envelope and
nucleolus begin to re-form
around
chromosomes.
• Cell devides forming 2
separate haploid cells

11. Meiosis II- Prophase II
• Chromosomes coil and
become compact if they
uncoiled during
Telophase I.
• The nuclear envelope
and nucleolus begin to
disappear.
• The Centrioli move to
opposite poles, forming
spindle fibres in
between them.

12. Meiosis II- Metaphase II
• The individual
duplicated chromosome
align along the equator.
• One chromosome per
spindle fibre are
attached by means of
the centromere.
• The Centrioli has
reached the opposite
poles.

13. Meiosis II- Anaphase II
• The spindle fibres
contract causing
duplicated chromosome
to split in half.
• These daughter
chromosomes begin to
move towards opposite
poles

14. Meiosis II- Telophase II
• Daughter chromosome
reach the opposite poles.
• The two cells invaginate
and form four daughter
haploid cells
• They uncoil and form a
chromatin network.
• Nuclear envelope and
nucleolus form around
chromatin network again.

16. Difference between meiosis I and
meiosis II
Meiosis I Meiosis II
Begins with Interphase= DNA Replication Begins with Prophase= No DNA
replication
Begins with Diploid number of
chromosomes
Begins with haploid number of
chromosomes.
Prophase consists of crossing over Prophase consists of no crossing over.