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Cell Division and Reproduction Asexual and Sexual reproduction By : D. Reis

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Asexual Reproduction A single organism produces offspring with identical genetic information

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Sexual Reproduction Haploid (n=23) sperm cell fertilizes a haploid (n=23) egg cell to produce a dipolid (2n=46) zygote.

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Sexual Reproduction Cells of the human body have 46 chromosomes When fertilization occurs a sperm and egg cell combine their chromosomes to make a zygote with 46 chromosomes. How is this possible?

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Meiosis The division of cells to produce specialized sperm and egg cells The division of cells to produce specialized sperm and egg cells 46 23 23 23232323 23

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Phases of Meiosis Assume DNA replication occurs prior to meiosis I Assume DNA replication occurs prior to meiosis I Prophase I Prophase I Metaphase I Metaphase I Anaphase I Anaphase I Telophase I Telophase I Prophase II Prophase II Metaphase II Metaphase II Anaphase II Anaphase II Telophase II Telophase II

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Homologous Chromosomes Paired chromosomes similar in shape, size, gene arrangement and gene information. Paired chromosomes similar in shape, size, gene arrangement and gene information. Each somatic cell contains 23 pairs of homologus chromosomes, or 46 in total Each somatic cell contains 23 pairs of homologus chromosomes, or 46 in total

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Stages of Meiosis I PROPHASE I Nuclear membrane dissolves Nuclear membrane dissolves Centrioles move to opposite poles Centrioles move to opposite poles Formation of spindle fibers Formation of spindle fibers

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Stages of Meiosis I PROPHASE I- PROPHASE I- Homologus chromosomes pair up in a process called synapsis and crossing over occurs

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Crossing Over/ Genetic Recombination The exchange of genetic material between two homologus chromosomes leads to genetic variability. The exchange of genetic material between two homologus chromosomes leads to genetic variability. Tetrad a pair of homologus chromosomes composed of 4 chromatids. Tetrad a pair of homologus chromosomes composed of 4 chromatids.

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Stages of Meiosis I METAPHASE I- METAPHASE I- Homologus chromosomes line up at the equatorial plate.

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Stages of Meiosis I ANAPHASE I- Spindle fibers shorten, the homologus chromosome pairs move toward opposite poles. THE SISTER CHROMATIDS DO NOT PULL APART AS THEY DO IN MITOSIS. ANAPHASE I- Spindle fibers shorten, the homologus chromosome pairs move toward opposite poles. THE SISTER CHROMATIDS DO NOT PULL APART AS THEY DO IN MITOSIS. 23 duplicated chromosomes move to opposite poles. 23 duplicated chromosomes move to opposite poles. TELOPHASE I- Two new genetically different haploid daughter cells are formed each containing 23 double stranded chromosomes TELOPHASE I- Two new genetically different haploid daughter cells are formed each containing 23 double stranded chromosomes Formation of nuclear membrane Formation of nuclear membrane

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Stages of Meiosis II PROPHASE II Nuclear membrane dissolves, spindle fibers form and centrioles move to opposite poles. PROPHASE II Nuclear membrane dissolves, spindle fibers form and centrioles move to opposite poles. METAPHASE II Spindle fibers attach to the chromosomes and the chromosomes (2 sister chromatids) align along the equatorial plate. METAPHASE II Spindle fibers attach to the chromosomes and the chromosomes (2 sister chromatids) align along the equatorial plate.

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Stages of Meiosis II ANAPHASE II Sister chromatids separate and move to opposite poles. ANAPHASE II Sister chromatids separate and move to opposite poles. TELOPHASE II Chromatids arrive at each pole and cell division begins. TELOPHASE II Chromatids arrive at each pole and cell division begins.

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Meiosis 1. Homologus chromosomes: 23 paternal and 23 maternal 2. Chromosomes are replicated and attached at the centromere

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Meiosis 3. Meiosis I reduction stage- Separation of homologus chromosomes 4. Meiosis II- separation of sister chromatids

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Results of Meiosis 4 gametes/reproductive cells which contain 23 chromosomes Haploid-each cell contains half the number of chromosomes from the parent cell All 4 cells are genetically different

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Results of Meiosis

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Oogenesis- the production of egg cells in females Spermatogenesis - the production of sperm cells in males

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Mitosis and Meiosis Compared

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Mitosis and Meiosis Compared Mitosis 2 daughter cells are produced 2 daughter cells are produced Daughter cells are diploid Daughter cells are diploid Daughter cells are the same as parent cells Daughter cells are the same as parent cellsMeiosis 4 daughter cells are produced 4 daughter cells are produced Daughter cells are haploid Daughter cells are haploid Daughter cells are genetically different from parent cells Daughter cells are genetically different from parent cells