Meiosis lecture notes Timed quiz Micrographs Mitosis / meiosis comparison.
Meiosis
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Transcript of Meiosis
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MEIOSISHonors Biology
Spring 2013
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Warm-Up With a neighbor, discuss the following:
What is meiosis? How does it differ from mitosis?
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Essential QuestionsWhat is meiosis and why is it necessary?
What are the stages of meiosis?
How does meiosis compare to mitosis?
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Haploid vs. DiploidDiploid cells
1. Body cells2. Contains homologous chromosomes3. 2N
B. Haploid cells1. Sex cells2. contains one member of each pair3. 1N
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Meiosis Meiosis– process which reduces by half the
number of chromosomes in a diploid cell
• meiosis occurs in sex organs of individual
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Overview of MeiosisA. Meiosis - formation of sex cells
1. Meiosis is cell division that results in a gamete containing half the number of chromosomes of its parent.2. Meiosis includes 2 steps that each closely resemble corresponding steps in mitosis.
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Phases of Meiosismeiosis I•Prophase I•Metaphase I•Anaphase I•Telophase I &?•Cytokinesis PMAT I
Meiosis II•Prophase II•Metaphase II•Anaphase II•Telophase II &?• Cytokinesis PMAT II
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Meiosis 1Meiosis I - reduction division
1. Interphase I2. Prophase I3. Metaphase I4. Anaphase I5. Telophase I
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Meiosis 1: Prophase 1–chromatin condenses to form chromosomes–homologous chromosomes attach to form tetrads
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Meiosis 1: Prophase 1– when tetrads
form, crossing over can occur
– crossing over is the
exchange of part of
homologous chromatids
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Meiosis 1: Metaphase 1
–tetrads line up on equator–spindle fibers attach to centromeres
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Meiosis 1: Anaphase 1– homologous
chromosomes separate– spindle fibers
pull them to opposite
poles
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Meiosis 1: Telophase and Cytokinesis
• telophase I– nuclear
membrane reforms
• cytokinesis– cytoplasm
splits
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Meiosis 1: Results• results– two haploid (n)
daughter cells = ½ the
number of chromosomes as
parent cell
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Meiosis IIMeiosis II - separation of chromatids
1. Interphase II2. Prophase II3. Metaphase II4. Anaphase II5. Telophase II
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–chromosomes already formed
Meiosis II: Prophase II
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–chromosomes line up along equator
Meiosis II: Metaphase II
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–sister chromatids separate–move to opposite ends
Meiosis II: Anaphase II
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•telophase II–nuclear envelope reforms
•cytokinesis–cytoplasm splits
Meiosis II: Telophase and Cytokinesis
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Meiosis II: Results– 4 haploid (n) daughter cells– all genetically different
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Ploidy
parent cell?•dipliod (2n)after meiosis I?•haploid (n) (monopliod)after meiosis II?•hapliod (n)
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Purpose of Meiosis: Diversity
Meiosis and sexual reproduction significantly contribute to genetic variation among offspring.
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Purpose of Meiosis: Gametes
• role of meiosis is to produce gametes
• meiosis in males– spermatogenesis– produces 4 sperm cells
• meiosis in females– oogenesis– produces 1 ovum (egg cell) and 3
polar bodies
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Where Does Meiosis Occur?
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Mitosis vs. Meiosis where does is occur?• meiosis – sex organs; mitosis – somatic cells number of cell divisions?• meiosis – 2; mitosis – 1 number of cells produced?• meiosis – 4; mitosis – 2 ploidy of daughter cells?• meiosis – hapliod (n); mitosis – dipliod (2n) # of chromosomes compared to parent cell?• meiosis – ½ # chromosomes; mitosis – same
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Mitosis vs. Meiosis