1. It’s MEIOSIS!

2. Vocab..
Cell cycle: Interphase (G1, S, G2), mitosis (cell division) and cytokinesis (pinching off into two cells)
Mitosis- division of cells producing 2 IDENTICAL cells (somatic or autosome cells – skin, heart, liver)
Gamete- sperm and egg
Zygote- fertilized egg cell
Haploid- half chromosomes (23)
Diploid- all chromosomes (46)
Chromosome- 2 chromatids (strands) and centromere (center)

3. Mitosis Review Prophase- start to divide Metaphase- line up in middle
Anaphase- centromeres break apart
Telophase- everything is identical on both ends and starts to form into two
Cytokinesis- final pinching off of 2 identical cells
** remember mitosis produces identical cells, so each parent cell has 46 chromosomes, baby has 46 chromosomes***

5. Meiosis Meiosis- division of sex cells (sperm and egg)
Produces gametes with half the number of chromosomes so when baby forms he/she has half from mom and half from dad

6. Meiosis Process
Involves 2 divisions: meiosis 1 and meiosis 2 (each broken into PMAT)

7. Starts with homologous pairs that DO NOT break apart until meiosis 2
Results in 4 haploid cells, each having half the number of chromosomes (zygote- half from mom and half from dad)

8. Meiosis contributes to genetic variation
1) Independent assortment- random homologous chromosomes

9. 2) Crossing over
Prophase 1- crossing over occurs (portion of one chromosome switcher onto another, producing diversity)

10. 3) Random fertilization
The sperm that fertilizes the egg is simply by chance

11. Importance of genetic variation
Meiosis is essential to evolution- No genetic process generates variation more readily
Pass on learned traits
Creates diversity

12. Meiosis results in gametogenesis
Gametogenesis- formation of gametes

13. Spermatogensis Spermatogenesis- formation of male sperm
Diploid cell increases in size and shape and becomes a large immature cell called a germ cell
Cell undergoes meiosis 1 resulting in 2 cells
2 cells undergo meiosis 2 forming 4 haploid cells
ALL 4 of the haploid cells grow a tail and become sperm
Each sperm is genetically different
Sperm is produced throughout a man’s reproductive years

15. Oogenesis Oogenesis- forming eggs in female
During meiosis 1 the cytoplasm divides unevenly, one cell gets most of the cytoplasm and this will become the EGG
Larger cell undergoes meiosis 2, division is uneven again, the larger cell becomes an ovum
Ovum- egg ready for fertilization
Other cells produced become polar bodies- cells that just get reabsorbed into the human body

16. Oogenesis continued
Egg development begins before birth, during embryonic development cells divide by mitosis to produce 2 million immature egg cells
Ovaries of a newborn contain all the eggs a female will ever have
During puberty egg cells complete meiosis 1
Once egg is fertilized, egg undergo meiosis 2

18. Reproduction Two types: Asexual reproduction- 1 parent
a. produces clones
b. prokaroytes (bacteria)- binary fission
c. eukaryotes
- fragmentation (planaria) body breaks into
two pieces and develop
- budding (hydra) new offspring splits from
existing one

19. Fragmentation (planaria)

20. Budding (hydra)

21. 2) Sexual Reproduction-
- two parents forming haploid gametes combine to form a fertilized egg (zygote)
- offspring has a combination of traits from mom and dad

22. Sexual versus Asexual Pro - produce many organisms in a short time Con
Asexual Reproduction
Pro
- produce many organisms in a short time
Con
- no variation, can NOT adapt
Sexual Reproduction
Pro
- different combination of genes, able to adapt
Con
- long period of time