1. Meiosis
Gamete Production

2. Meiosis Similar in many ways to mitosis Several differences however
Involves 2 cell divisions
Results in 4 cells with 1/2 the normal genetic information.
Vocabulary:
Diploid (2N) - Normal amount of genetic material
Haploid (N) - 1/2 the genetic material.

3. Meiosis In Humans, these are the Ova (egg) and sperm.
Meiosis results in the formation of haploid cells.
In Humans, these are the Ova (egg) and sperm.
Ova are produced in the ovaries in females
Process is called oogenesis
Sperm are produced in the testes of males.
Process is called spermatogenesis
Meiosis occurs in 2 phases: Meiosis I & Meiosis II

4. Spermatogenesis & Oogenesis
Sperm formation
Egg formation

5. Why Do we Need Meiosis?
It is the fundamental basis of sexual reproduction
Two haploid (n) gametes are brought together through fertilization to form a diploid (2n) zygote

6. Fertilization – “Putting it all together”

7. Meiosis I
Prior to division (S phase), amount of DNA doubles

8. Replication of Chromosomes
Replication of DNA occurs
Occurs prior to division (S of Interphase)
Replicated copies are called sister chromatids
Held together at centromere
Occurs in Interphase
Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere.

9. Prophase I Genes are exchanged at these connections
Areas of homologous chromosomes connect at areas called CHIASMATA
Genes are exchanged at these connections

10. Prophase I Homologous (same genes, different alleles)
Gene X
Sister Chromatids
(same genes,
same alleles)
Homologous
(same genes, different alleles)

11. Crossing Over
Segments of homologous chromosomes break and reattach at similar locations.
Results in new genetic combinations of offspring.
This is the main advantage of sexual reproduction

13. Chiasmata

14. Anaphase I
During Anaphase I, each HOMOLOGOUS CHROMOSOME is pulled to opposite sides of the cell.
Unlike mitosis, the CENTROMERES DO NOT BREAK.
Nuclei reform in Telophase I
CYTOKENESIS occurs, results in 2 cells, but these cells still contain sister chromatids paired together.

15. Meiosis II DNA DOES NOT double
Chromosomes randomly line-up along metaphase plate like regular mitosis.
During Anaphase II, CENTROMERES BREAK and each SISTER CHROMATID is pulled to opposite sides of the cell.
Nuclei reform and cytokinesis usually occurs (although it is often unequal).
Sister chromatids

16. Meiosis: Two Part Cell Division
Sister
chromatids
separate
Homologous Chromosomes
separate
Meiosis I
Meiosis II
Diploid
Diploid
Haploid

17. Overview of Meiosis