introduction about meiosis stages of meiosis difference between meiosis and mitosis significance conclusions

1. MEIOSIS

2. CONTENTS
1) INTRODUCTION
2) STAGES OF MEIOSIS
3) DIFFERENCE BETWEEN MEIOSIS
AND MITOSIS
4) SIGNIFICANCE
5) CONCLUSIONS

3. INTRODUCTION
• Meiosis is a special type of cell division in the
eukaryotes that reduces the number of
chromosome in the parent cell by half and
produce four gamete cell.
• Meiosis was discovered by German biologist
Oscar Hertwig in sea urchin eggs in 1876.
• The term meiosis was coined by J.B Farmer
and J.B Moore in 1905
• The process of meiosis is divided into two
phase, meiosis I and meiosis II

4. STAGES OF MEIOSIS
• Before a dividing cell enters meiosis it
undergoes a period of growth called
interphase. Interphase is of:-
• G1 phase :- The period prior to synthesis of
DNA. In this phase the cell increases in mass in
preparation for cell division.
• S phase :- The period during which DNA is
synthesized.
• G2 phase :- The period after DNA synthesis
but prior to the start of prophase.

5. MEIOSIS I
• PROPHASE I
• It is the longest phase
of meiosis.
• DNA coils tightly and the individual chromosomes
becomes visible under light microscope.
• Homologus chromosomes becomes associated in
synapsis and they exchange segment by crossing
over.
• Prophase I is divided into 5 sub stages namely,
leptotene, zygotene, pachytene and diakinensis.

6. SUB STAGES OF PROPHASE I
• LEPTOTENE/ LEPTONEMA(thin threads)
• The chromosomes have
appeared but are not yet fully
condensed and becomes visible.
• During leptotene lateral
elements of synoptemal
complex assembles.

7. • ZYGOTENE/ZYGONEMA ( paired threads)
• Chromosomes continue to
become denser.
• Homolog's begins to unite by
coming into appropriate
alignment referred to as rough pairing.
• Synapsis takes place.

8. • PACHYTENE/PACHYNEMA ( thick threads)
• Coiling and shortening continues
as the chromosomes becomes
more condensed.
• A synapsis is formed between them forming a
tetrad.
• Crossing over takes place.

9. • DIPLOTENE/DIPLONEMA ( two threads)
• The chromosomes uncoils a bit
allowing some transcription of
DNA.
• The homologus chromosome of
each bivalent remains tightly bound at
chiasmata.
• Synoptemal complex degrade and
homologous chromosome separate from one
another.

10. • DIAKINENSIS (moving through)
• Nucleolus disappears, terminalization reaches
completion.
• It is the 1st point in meiosis
where the four parts of tetrad are actually
visible.
• Nuclear envelope breaks down and the
spindle fibres begins to interact with the
tetrad

11. METAPHASE I
• The nuclear membrane has
disappeared and the
microtubules forms spindle.
• The spindle fibre attach to
only one side of the
centromere and two
homologous attach to the
microtubles orienting from
opposite pole.
• Each pair of homologous chromosomes then line up to
the metaphase plate.
• Either maternal or paternal homolog may orient
towards a given pole.

12. ANAPHASE I
• The microtuble of the spindle
fibre shorten and pull the
chromosome towards the
pole, taking both sister
chromatid with them.
• Each pole ends up with a complete set of
chromosome consisting of one member of the
homologous pair.

13. TELOPHASE I
• The first meiotic
division effectively
ends when the
chromosome
arrive at the pole.
• The nuclear
membrane reforms around the daughter nuclei.
Each daughter nucleus contain two sister
chromatid attached to the common centromere.
• Because of crossing over the two sister chromatid
are not identical.

14. MEIOSIS II
• Meiosis II is the second part of meiotic
division also known as equational division, the
end result of which produce 4 haploid cell.
• PROPHASE II
• The nuclear envelope and
nucleoli breaks down again
as well as shortening and
thickening of the chromatid.
• Formation of spindle fibre is initiated again.

15. • METAPHASE II
• Spindle fibre binds to
both side of the
centromere.
• The new equatorial
metaphase plate is rotated
by 90˚ when compared to meiosis I,
perpendicular to previous plate.

16. • ANAPHASE II
• The spindle fibres
contracts and the sister
chromatids move
towards opposite pole.
• Each pole ends up with 2 sets of
chromosomes.

17. • TELOPHASE II
• The chromosome reach
opposite pole.
• Uncoiling and lengthening
of the chromosome and the
disappearance of spindle fibre takes place.
• Nuclear envelope reforms around the sets of
daughter chromosome.
• Meiosis is now complete and ends up with 4
daughter cell.

18. SIGNIFICANCE OF MEIOSIS
• To produce genetic variation among offspring.
• To ensure production of haploid gametes in
sexual reproduction.
• To maintain diploid number in each
generation.
• To allow trait inheritance in offspring.

19. DIFFERENCES BETWEEN MEIOSIS AND
MITOSIS
• Meiosis is a type of cellular reproduction in
which the number of chromosome is reduced
to half whereas mitosis is an asexual
reproduction in which the cell divides into two
producing replica with equal number of
chromosome.
• Pairing of homologous chromosome takes
place in meiosis but not in mitosis.
• Number of haploid daughter cell produce in
meiosis is 4 and 2 in case of mitosis.

20. CONCLUSIONS
• The process of meiosis is an important event
that occurs in sexually reproducing plants and
animals where the number of chromosome is
reduced to half.
• Meiosis maintains the diploid number of
chromosme in each generation.

21. THANK YOU