1. Cell Division
Meiosis

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: cell division in two parts
Sister
chromatids
separate
Haploid
Diploid
Meiosis I
(reduction
division)
Meiosis II
Chromatids
separate
(equational
division) 2n n n
Result: one copy of each chromosome in a gamete.

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

6. What are Homologous chromosomes?
sister
chromatids
sister
chromatids

7. Chromosomes condense forming Tetrads. -Nuclear envelope fragments.
Prophase I 1 2
Late prophase
-Homologous
Chromosomes condense forming Tetrads.
-Spindle forms.
-Nuclear envelope fragments.
Early prophase
Chromatids pair up.
Crossing over occurs.

8. Metaphase I (Homologous) Chromatid pairs align
along the equator of the cell.

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

10. Telophase I Nuclear envelopes reassemble. Spindle disappears.
Cytokinesis divides cell into 2

11. Meiosis II Gene X Sister chromatids carry identical genetic
Meiosis II produces gametes with
one copy of each chromosome and thus one copy of each gene.
Sister chromatids carry
identical genetic
information.

12. Meiosis II : the equational division
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
Individual chromatids separate
and move to opposite poles.

16. Telophase II Nuclear envelope assembles. Chromosomes unravel.
Spindle disappears.
Cytokinesis divides cell into 2.

17. Results of meiosis
Four haploid cells
One copy of each chromosome

18. “Putting It All Together” - Fertilization

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

20. Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
Where
Somatic cells
Sex cells
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction

21. 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

22. Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Sperm become streamlined and motile.
Sperm primarily contribute DNA to an embryo.
Eggs contribute DNA, cytoplasm, and organelles to an embryo.
During meiosis, the egg gets most of the contents; the other cells form polar bodies.