1. Cell Division

2. Meiosis
Meiosis occurs in sexual reproduction when a diploid germ cell produces four haploid daughter cells that can mature to become gametes (sperm or egg).

3. Meiosis Goal: reduce genetic material by half
Why? n (mom) + n (dad) = 2n (offspring)
from mom
from dad
child
too
much!
meiosis reduces
genetic content
Just right!

4. Meiosis: 2 part cell division
Sister
chromatids
separate
Haploid
Diploid
Meiosis I
Meiosis II
Homologous Chromosomes pairs separate 2n n n
Result: one copy of each numbered chromosome in a gamete.

5. Meiosis I Prophase I (early) (diploid) (late) Metaphase I Anaphase I
Telophase I
Nucleus
Spindle
fibers
Nuclear
envelope

6. Nuclear envelope breaks apart
Prophase I Early
Early prophase
Chromosomes condense
Spindle forms
Nuclear envelope breaks apart .

7. Chromatids pair (synapse)
Prophase I Late
Late prophase
Chromatids pair (synapse)
Crossing over occurs between chromatids
of the homologous chromosome pair

8. Metaphase I
Homologous chromosome pairs
line up on the cell’s equator

9. Anaphase I Chromosomes separate and move to opposite poles.
Sister chromatids remain
Attached at their centromeres.

10. Telophase I Nuclear envelopes reforms Spindle disappears.
Cytokinesis divides cell into two

11. Meiosis II Sister chromatids have carry different genetic information
End product of meiosis is Each Sex cell /gamete has :
1 copy of each chromosome
1 copy of each gene segment
Sister chromatids have carry
different genetic information
due to crossing over

12. Meiosis II Prophase II (haploid) Metaphase II Anaphase II Telophase II
Four
Non-identical
haploid
daughter cells

13. Prophase II
Nuclear envelope fragments.
Spindle forms.

14. Metaphase II
Chromosomes align
along equator of cell.

15. Anaphase II
Sister chromatids separate
and move to opposite poles.

16. Telophase II Nuclear envelope assembles. Chromosomes unravel.
Spindle disappears.
Cytokinesis divides cell into two.

17. Results of meiosis Four haploid cells One copy of each chromosome
Not the same genes on each chromosome

18. “Putting It All Together” - Fertilization

19. What Meiosis is About
Meiosis allows the creation of unique individuals
through sexual reproduction.
Meiosis Video Link

20. Meiosis Video Link #1
Meiosis Video Link #2
Meiosis Video Link#3

21. 2 diploid 4 haploid
Crossing over between nonsister chromatids
Reduction divisiion
Increases genetic variability vs. clones
Meiosis 1 Homologous chrom separate
Meiosis 2 Sister chromatids separate

22. Mitosis Meiosis Number of divisions 1 2
Number of daughter cells made through process 4
Are the new cells Genetically identical?
Yes No
# of Chromosomes compared to parent cell
Same as parent
Half of parent
What cell go thru this division process
Somatic cells
Sex cells
When do cells got thru this division process
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction

23. MITOSIS MEIOSIS Occurs in somatic (body) cells
Occurs only in gonads (sex organs: ovary/testes)
Produces cells for repair,
maintenance, growth, asexual reproduction
Only produces gametes (sex cells: egg/sperm)
Results in identical diploid (2n) daughter cells
Reduction division results in haploid (n) cells

24. Meiosis II produces gametes with
one copy of each chromosome and thus one copy of each gene.