2. Sexual Reproduction Sexual reproduction involves the production of specialized cells (gametes) and the fusion of their nuclei (fertilization ) producing a fertilized egg cell (zygote). The zygote undergoes mitotic cell division during its growth and maturity.

3. Gametogenesis Each body cell of an organism contains the diploid (2n) number of chromosomes characteristic of that species. These chromosomes are present in homologous pairs. Homologous chromosomes contain genes for the same traits. Gametogenesis is the process in which gametes are produced. It involves meiotic cell division and cell maturating. This process occurs in specialized organs called gonads. Some organisms have only male or female gonads while others have both, such as the earthworm and hydra are called hermaphrodites. The result of gametogenesis is the production of sperm (in the male) or egg cells (in the female) which have half (n) the number of chromosomes of a normal body cell (2n). Monoploid = Haploid

4. Meiosis The chromosome number is reduced by one-half and monoploid (n) nuclei which contain one chromosome of each homologous pair. Meiosis has two separate and distinct divisions.

5. Meiosis Sexual Reproduction only (gametes) Occurs in Animals & Plants

6. Interphase Cells performing life functions. Chromosomes replicate before division cycle begins. Each single-stranded chromosome results in a pair of identical sister chromatids. Centrioles

7. Prophase I (Synapsis) Nuclear membrane and Nucleolus disappear Homologous Tetrads (group of 4 chromatid strands) synapse or pair up Spindle fiber starts to form

8. Metaphase I (alignment) Homologous Tetrads attach to spindle fibers and align at the Equator

9. Anaphase I (disjunction) Homologous Tetrads disjunct (split apart) at their centromeres to opposite poles

10. Telophase I Homologus chromosomes separate farther toward poles Nuclear membrane and Nucleolus start to reappear

11. Cytokinesis Cell membrane pinches in and divides the cytoplasm in animal cells Cell plate forms in plant cells to divide cytoplasm Two daughter cells formed

12. IPMAT-II Interphase II does NOT replicate the chromosomes again. Think of it as organization. Prophase II, Metaphase II (centromeres replicate), Anaphase II, and Telophase II involve the same process as IPMAT I, however, we are dividing Sister Chromatids. After the second Cytokinesis, we end up with 4 new cells, each having only half the original chromosomes.

13. Meiosis Second Division Prophase 2Metaphase 2Anaphase 2Telophase 2 Cytokinesis 2

14. Summary Mitosis is associated with growth/repair and asexual reproduction. Meiosis is associated with sexual reproduction. As a result of Mitosis cell division, the daughter cells are identical to the original cell. As a result of Meiosis cell division, the resulting cells have only one-half (n) the number of chromosomes of the original parent cell.

15. Gametogenesis Spermatogenesis – male gonads, testes, produce male gametes, sperm. The primary sex cell undergoes meiosis and produces four monoploid cells, each matures into a motile sperm cell called the spermatozoa. Oogenesis – female gonad, ovary, and the gamete is the ovum (egg). Larger than sperm, contains stored nutrients in form of yolk. Only one monoploid egg cell forms from meiosis and maturation. The other cells, polar bodies, degenerate. *Starts at puberty and continues for most of life thereafter *All female oogenesis done before birth

16. Human Gametogenesis Continuation Of Life Video

17. Meiosis in Humans

18. Mitosis -vs- Meiosis Animation