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Three Phases of Interphase
- G1: Growth, Transcription, Translation
- G2: DNA replication (x2 DNA)
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Phases of Cell Division (M Phase)
- 1. Prophase
- 2. Metaphase
- 3. Anaphase
- 4. Telophase
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Somatic Cells
- Cells of the body except gametes
- Diploid (2N)/ Two sets of chromosomes
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Prophase 2N
- 4 visible chromosomes -> each have two sister chromatids
- Nuclear enveloppe
- "Spaghetti" Random positioning of chromosomes
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Centromere
Holds two sister chromatids
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Metaphase
- Kinetochore plate anchors chromosome to mitotic spindle
- Individual chromosomes align at metaphase plate (equator)
- Line up in single file
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Anaphase
- Chromatids separate and move to opposite poles (now called chromosomes)
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Telophase
- Cytokinesis: Division of Cytoplasm
- Cleavage furrow
- Nuclear enveloppe reforms
- Two Identical daughter cells in interphase
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Telophase in Plants
- Cytokenesis: Vesicles from the golgi fuse together at the metaphase plate (equator)
- Formation of cell plate
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Meiosis in animals:
Phases:
formation of...
2 Nuclear Divisions
- 1. Prophase I
- 2. Metaphase I
- 3. Anaphase I
- 4. Telophase I
- 5. Prophase II
- 6. Metaphase II
- 7. Anaphase II
- 8. Telophase II
Gametes (sperm, egg)
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Meiosis: Prophase I
- Synapsis: Joining of homologous chromosomes -> tetrads
- Crossing over: Homologues exchange genes
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Meiosis: Metaphase I
- Tetrads align at Metaphase plate
- Independent assortment: members of pair align randomly
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Sources of genetic variation in Meiosis
- 1. Crossing over: random exchange of genes when forming tetrads (prophase I)
- 2. Independent assortment: members of a pair align randomly
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Meiosis: Anaphase I
- Tetrads separate from eachother, move to opposite poles
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Meiosis: Telophase I
- Cytokenesis
- N = 2 chromosomes each with 2 chromatids
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Meiosis II is Similar to Mitosis
Telophase II produces...
4 different haploid cells
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Production of sperm cells occurs in
Testes -> seminiferous tubules
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Sperm production process
Spermatogonium -> primary spermatocyte -> secondary spermatocyte -> sperm cell
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Haploid or Diploid?
1. Spermatogonium
2. Primary Spermatocyte
3. Secondary Spermatocyte
4. Sperm Cell
- 1. Diploid 2N
- 2. Diploid 2N
- 3. Haploid N
- 4. Haploid N
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Mitosis, Meiosis I or Meiosis II?
1. Spermatogonium-> Primary Spermatocyte
2. Secondary Spermatocyte-> Sperm Cell
3. Primary Spermatocyte-> Secondary Spermatocyte
- 1. Mitosis
- 2. Meiosis II
- 3. Meiosis I
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Characteristics of Spermatogenesis
- Even cytokenesis: Equal division of cytoplasm
- Numerous
- Continuous production
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Production of an ovum occurs in
Ovary
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Ovum production process:
Primary oocyte -> Secondary Oocyte & First polar body (Meiosis I) -> continues if fertilized
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When do the following occur?
1. Primary oocyte -> Secondary oocyte & 1st polar body (Meiosis II)
2. Seconday oocyte -> ovulation (meiosis II)
- 1. Before birth
- 2. Puberty or later
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Characteristics of Oogenesis
- Not continuous (interrupted developement)
- -Woman stats oogenesis before birth
- -"Egg supply" arrested in meiosis I as primary oocytes
- -Secondary oocytes and 1st polar body have same amount of genetic info, but not same amount of cytoplasm
- -At ovulation secondary oocyte is arrested in meiosis II
- -Meiosis II never finished unless fertilized
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Embryology developement process
Early cleavage -> Morula -> Blastula -> Gastrula
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Early Cleavage:
Rapid cell divsion (mitosis) with no cellular growth
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Morula
- Solid mass
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Blastula
Blastocoel cavity (blastocyst in humans)
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Gastrula
 - Archenteron= primitive gut -> digestive tract
- 3 germ layers: ectoderm, mesoderm, endoderm
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Germ layers functions
- Ectoderm: develops into brain, nervous system, skin
- Mesoderm: muscle, bone, blood -> heart
- Endoderm: Inside lining of organs
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