Meiosis
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Meiosis (Sex Cell Division)
What is Meiosis?
Cell division in which 1 Diploid Cell produces 4 Haploid cells. This makes 4 Genetically Different Cells. Has two divisions of the nucleus: – Meiosis 1 & Meiosis 2
Meiosis 1
Prophase 1 – – –
Chromosomes condense Nuclear envelope breaks down Homologous chromosomes pair up and “cross over”
What’s the point in Crossing Over?
Crossing Over – Occurs in Prophase 1 – Portions of chromosomes are exchanged
Causes genetic recombination
Metaphase 1 – Homologous chromosomes move to the middle (equator) of the cell – (moved by spindles)
Anaphase 1 – Homologous chromosomes separate *Chromatids do not separate at centromere!*
Telophase 1 – Chromosomes gather at poles – Nuclear envelope reforms – Cytoplasm divides
End of Meiosis 1 Two haploid cells formed
Meiosis 2
Repeat of Meiosis 1, but no crossing over in Prophase 2 In Anaphase 2, Centromeres divide The end result is 4 Haploid Cells
Prophase 2 – New spindle forms around chromosomes
Metaphase 2 – Chromosomes align in center – **Spindle fibers attach to centromeres**
Anaphase 2 – **Centromeres Divide** – Chromatids move to opposite poles
Telophase 2 – Nuclear envelope forms around chromosomes
Independent Assortment – Each pair of chromosomes separates independently – 223 ~ 8 million different gametes produced
Random fertilization – Since the zygote is made of two gametes…
223 x 223 = 64 trillion
Spermatogenesis occurs in males – Formation of sperm cells
Oogenesis – Formation of egg cells
What is Meiosis?
Cell division in which 1 Diploid Cell produces 4 Haploid cells. This makes 4 Genetically Different Cells. Has two divisions of the nucleus: – Meiosis 1 & Meiosis 2
Meiosis 1
Prophase 1 – – –
Chromosomes condense Nuclear envelope breaks down Homologous chromosomes pair up and “cross over”
What’s the point in Crossing Over?
Crossing Over – Occurs in Prophase 1 – Portions of chromosomes are exchanged
Causes genetic recombination
Metaphase 1 – Homologous chromosomes move to the middle (equator) of the cell – (moved by spindles)
Anaphase 1 – Homologous chromosomes separate *Chromatids do not separate at centromere!*
Telophase 1 – Chromosomes gather at poles – Nuclear envelope reforms – Cytoplasm divides
End of Meiosis 1 Two haploid cells formed
Meiosis 2
Repeat of Meiosis 1, but no crossing over in Prophase 2 In Anaphase 2, Centromeres divide The end result is 4 Haploid Cells
Prophase 2 – New spindle forms around chromosomes
Metaphase 2 – Chromosomes align in center – **Spindle fibers attach to centromeres**
Anaphase 2 – **Centromeres Divide** – Chromatids move to opposite poles
Telophase 2 – Nuclear envelope forms around chromosomes
Independent Assortment – Each pair of chromosomes separates independently – 223 ~ 8 million different gametes produced
Random fertilization – Since the zygote is made of two gametes…
223 x 223 = 64 trillion
Spermatogenesis occurs in males – Formation of sperm cells
Oogenesis – Formation of egg cells
