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Quick review: identify this stage of the diploid cell cycle.
• Defined: Process where the chromosome number is reduced by half
• Gametes created (egg & sperm)
• End Result: Four Haploid Cells
• Similar as mitosis, except…• Two Events:
– 1) Synapsis: Pairing of homologous chromosomes
– Dad’s #1 chromosome pairs with Mom’s #1, etc…– The four paired chromatids equals a TETRAD
– 2) Crossing Over: Exchange of genes
Mom 1
Dad 1
Synapsis
dad
mom
mom
dad
dad
mom
Spindle fibers pull homologous chromosomes together
tetrad
tetrad
tetrad
• Cytokinesis divides the cells• Each cell contains 1 of the
homologous chromosomes
mom
dadm
om
dad
dadm
om
• Cytokinesis divides the cells• Nucleus reforms on the four new cells• Chromatids uncoil• End Result: Four haploid cells
• Defined: Production of sperm cells
• Location: male testes• Makes final changes
to sperm cell• Four haploid sperm
cells at a time
Meiosis 1
Meiosis 2
Spermatogenesis
spermatogonium
• Defined: Production of the egg cell (ovum)– In female ovaries
• During meiosis I: Cytoplasm distributed unequally
• After meiosis II:
– 1 cell matures
– 3 “Polar Bodies” dissolve
Meiosis 1
Meiosis 2
Oogenesis
oocyte
• Division of somatic cells
• Ex: Blood cells, skin cells, nerve cells…
• End Result: 2 Diploid Cells
• Importance: Replaces aging cells
• Importance: Form of asexual reproduction
• Division of gametes
• Ex: Sperm and Egg cells
• End Result: 4 Haploid cells
• Importance: Reduces the gamete chromosome number by half
Kobe Kuiz
1) Name three ways that meiosis and mitosis differ.
2) Pick a stage of meiosis…any stage. Describe what happens in it.
3) What type of cells does meiosis create?
4) What are homologous chromosomes?
5) When do homologous chromosomes move to opposite ends of the cell?
6) When do chromatids move to opposite ends of the cell?
7) Why is no DNA created in meiosis 2?
8) How does meiosis differ in males vs. females?