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Bellwork Draw this in your notes and fill in the phases of mitosis
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MEIOSIS Unit 6
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Terms to Know Homologous Chromosomes – corresponding (matching) chromosomes from a female and male parent. -Each pair of homologous chromosomes has genes for the same traits Diploid Cell (2n) – a cell with two of each kind of chromosome Haploid Cell (n) – a cell that contains one set of the same kind of chromosomes Sexual reproduction — reproduction involving the production and fusion of haploid sex cells Gene – segment of DNA that codes for a trait Replicated Chromosome – a chromosome that has doubled it’s DNA Non-Replicated Chromosome – a chromosome that has split and contains only one copy of DNA.
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What is Meiosis and why do we need it? A form of cell division happening in sexually reproducing organisms consisting of two consecutive cell divisions (meiosis I and meiosis II). Meiosis produces 4 haploid (n) sex cells Sperm—male gamete Egg—female gamete Meiosis: a kind of cell division, which produces gametes containing half the number of chromosomes as a parent’s body cell
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Meiosis Overview Meiosis I: One diploid cell (46 replicated chromosomes/23 pairs) becomes two cells Meiosis II: The two cells become 4 haploid cells These cells are not identical but they are very similar
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Why half the chromosomes in gametes? At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents
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Fertilization The haploid sperm (carrying 1 set of chromosomes) combines with the haploid egg (carrying 1 set of chromosomes). The result is a diploid zygote.
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Female vs. Male Oogenesis egg production Spermatogenesis Sperm Production
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What does Meiosis accomplish? 1. Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). 2. Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives through crossing over and independent assortment.
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Steps in Meiosis PMAT 2 similar cells 23 chromosomes Separates homologous pairs Haploid PMAT 4 similar cells 23 chromosomes Separates replicated chromosomes Haploid Meiosis I – starts diploidMeiosis II – starts haploid Same steps as Mitosis, divides twice to produce 4 daughter cells instead of 2. Daughter cells are not identical but similar
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Interphase Interphase Cells duplicate their DNA G1, S, G2
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Prophase I Prophase I sister chromatids pair up forming a homologous chromosome Crossing Over: When two chromosomes exchange portions of their chromatids (genetic material is swapped) Synapsis: the homologous chromosomes line up forming a four part structure called a tetrad. Crossing over during meiosis, increases the genetic variability due to allele combinations. – Genetic recombination is a major source of variation among organisms
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Metaphase I Metaphase I Spindle fibers attach to the centromeres on each chromosome Homologous chromosomes line up together.
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Anaphase I Anaphase I Spindle fibers pull the homologous chromosomes toward opposite ends of the cell.
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Telophase I/Cytokinesis Telophase I/Cytokinesis Meiosis I results in 2 haploid (n) daughter cells. Each with half the number of chromosomes as the original cell (23) Still replicated chromosomes.
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Prophase II Prophase II 2 haploid (n) daughter cells. Each with half the number of chromosomes as the original cell. Interphase does NOT happen again. Same steps as normal prophase.
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Metaphase II Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis. Occurs in BOTH cells.
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Anaphase II Anaphase II The sister chromatids separate and move toward opposite ends of the cell
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Telophase II / Cytokinesis Telophase II / Cytokinesis Opposite of prophase occurs, cytoplasm splits. END RESULT: four haploid (n), non-replicated, non- identical daughter cells.
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Mitosis vs. Meiosis Diploid 2n diploid 2n 46 chromosomes 46 chromosomes Replicated chromosomes Non-Replicated Chromosomes Somatic Cells Creates 2 identical cells 1 trip through PMAT Diploid 2n haploid n 46 chromosomes 23 chromosomes Replicated chromosomes Non-Replicated Chromosomes Gamete cells Creates 4 similar cells 2 trips through PMAT
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Meiosis Drawing Things to Label: Label each cell as diploid (2n) or haploid (n) Label the chromosome number of each cell Circle and label a homologous pair of chromosomes Circle and label a replicated chromosome. Circle and label a non-replicated chromosome.
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