Mitosis & meiosis Gametogenesis & fertilization References: Alberts, et al Molecular Biology of the Cell, 5 th ed., Garland Science, NY. Hickman, et al Integrated Principles of Zoology, 13 th ed., McGraw-Hill, NY. Hoefnagels, Mariëlle Biology, 1 st ed., McGraw-Hill, NY; Ch 8-9. Mader, Sylvia S Biology, 10 th ed., McGraw-Hill, NY; Ch 9-10.

The cell cycle G1G1 S G2G2 M

Cell cycle ●Interphase –G 1, S, G 2 ●Mitosis –Cytokinesis is division of 1 cell into 2. –Mitosis is separation of chromatids. ●In preparation for cytokinesis ●Chromatids are replicate chromosomes. G1G1 S G2G2 M

Figure 4-1 Molecular Biology of the Cell (© Garland Science 2008)‏

Mitosis & cytokinesis

Phases of mitosis ●Prophase –Chromatin condenses into chromosomes. ●Metaphase –Chromosomes line up across cell. ●Anaphase –Spindle fibers pull chromatids apart. ●Telophase –Chromosomes separate into daughter cells.

Ploidy doesn't change during mitosis. ●Ploidy: # of homologues –Homologues: versions of same chromosome –Don't confuse with chromatids ●Haploid (n) or diploid (2n) ●Parent cell is 2n daughter cells are 2n ●Parent cell is n daughter cells are n

Mitosis Metaphase 2n

Meiosis I Metaphase I Meiosis II Metaphase II 2n n n n n n n n

Meiosis ●Segregation of homologous chromosomes ●Into haploid gametes ●Meiosis I is the reduction division ●Meiosis II works like mitosis –(But the cells are already haploid)

Meiosis I (reduction division) ●Prophase I –Chromatin condenses into chromosomes. ●Metaphase I –Homologous pairs line up across cell. ●Anaphase I –Spindle fibers pull homologues apart. ●Telophase I –Chromosomes separate into daughter cells. ●Ploidy is reduced from 2n to n

Meiosis II ●Metaphase II –Chromosomes line up across cell. ●Anaphase II –Spindle fibers pull chromatids apart. ●Telophase II –Chromosomes separate into daughter cells. ●Parent and daughter cells are haploid.

Gametogenesis ●Spermatogenesis in mammals ●Oogenesis in mammals

Spermatogenesis in mammals ●Primary spermatocyte (2n) ●Secondary spermatocytes (n) ●Spermatids (n) ●Sperm (n)

Oogenesis in mammals ●Primary oocyte (2n) ●Secondary oocyte and polar bodies (1n)

Fertilization ●Ovum (1n) and sperm (1n) combine ●Zygote (2n) results

Fertilization and activation Prevention of polyspermy  Fast block Change in membrane potential.  Slow block Cortical reaction causes vitelline membrane to separate from cell membrane.

Figure From Hickman et al (13th ed.)‏