Mitosis & meiosis
Gametogenesis & fertilization
References:
Alberts, et al. 2008. Molecular Biology of the
Cell, 5th ed., Garland Science, NY.
Hickman, et al. 2006. Integrated Principles of
Zoology, 13th ed., McGraw-Hill, NY.
Hoefnagels, Mariëlle. 2009. Biology, 1st ed.,
McGraw-Hill, NY; Ch 8-9.
Mader, Sylvia S. 2010. Biology, 10th ed.,
McGraw-Hill, NY; Ch 9-10.
The cell cycle
G2
M
G1
S
The cell cycle
Cell cycle
● Interphase
M
G2
– G1, S, G2
● Mitosis
G1
S
– Cytokinesis is division of 1 cell into 2.
– Mitosis is separation of chromatids.
● In preparation for cytokinesis
● Chromatids are replicate chromosomes.
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
2n
2n
2n
Metaphase
2n
Meiosis I
n
n
Metaphase I
n
Meiosis II
n
n
n
n
Metaphase II
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 08.04
From Hickman et al. 2006 (13th ed.)