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Meiosis Formation of Sex Cells to Transfer Genetic Information to the Next Generation.

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Presentation on theme: "Meiosis Formation of Sex Cells to Transfer Genetic Information to the Next Generation."— Presentation transcript:

1 Meiosis Formation of Sex Cells to Transfer Genetic Information to the Next Generation

2 Mitosis and Meiosis in the Human Life Cycle Nuclear division reducing the chromosome number, leading to sperm or eggs Diploid number of chromosomes, two full sets Haploid number of chromosomes, one full set Nuclear division retaining the original chromosome number

3 Mitosis and Meiosis 2 Genetically-Identical Human Cells each with 46 chromosomes (DIPLOID) (DIPLOID) 4 Genetically-Different Human Cells each with 23 chromosomes (HAPLOID) (HAPLOID) Human Cell with 46 chromosomes (DIPLOID) Interphase Mitosis Cytokinesis Interphase Meiosis Cytokinesis

4 Homologous Chromosome Pairs Diploid cells have pairs of chromosomesDiploid cells have pairs of chromosomes Each homologous chromosome pair is genetically matched so that the genes are arranged in the same orderEach homologous chromosome pair is genetically matched so that the genes are arranged in the same order Meiosis distributes members of each pair to separate nucleiMeiosis distributes members of each pair to separate nuclei Humans have 1 pair of sex chromosomes and 22 pairs of autosomes

5 Cell Cycle With Meiosis G1 cytoplasm doubles, including organelles S chromosomes duplicate G2 synthesis of proteins and assembly of components for division cytokinesis Meiosis Interphase includes G1 = growth phase 1 S = synthesis phase S = synthesis phase G2 = growth phase 2 Interphase Meiosis II cytokinesis Meiosis I Meiosis includes two chromosomal divisions Meiosis I Meiosis II Cytokinesis = division of cytoplasmic contents

6 Applying Your Knowledge A.When does chromosomal division occur? B.When do the cytoplasmic contents double? C.When does chromosome duplication occur? 1.G1 phase 2.S phase 3.G2 phase 4.Meiosis I and II

7 Meiosis Involves Two Chromosomal Divisions Reduction Division: Separation of homologous chromosomes, reducing the chromosome number to haploid Equational Division: Separation of sister chromatids, no change in chromosome number

8 Duplicated Chromosomes in Early Meiosis Homologous Chromosome Pair Duplicated chromosomes joined at their centromeres Centromere = constricted region Nonsister Chromatids are joined to different centromeres

9 Prophase I of Meiosis I  Chromosomes thicken  Genetic exchange occurs between nonsister chromatids through crossing-over

10 Metaphase I of Meiosis I  Homologous pairs line up at the cell equator  Spindle fibers attached to centromeres cause chromosomal movement Spindle fiber

11 Anaphase I and Telophase I of Meiosis I Anaphase I  Members of homologous pair separate and are pulled to opposite poles of the cell Telophase I  Chromosomes reach opposite poles + cytokinesis Cytokinesis  Cytoplasm divides into two separate cells Daughter cells are haploid with duplicated chromosomes

12 Prophase II and Metaphase II of Meiosis II Prophase II  Chromosomes thicken Metaphase II  Chromosomes line up at cell equator

13 Anaphase II and Telophase II of Meiosis II Anaphase II  Sister Chromatids separate and move to opposite poles Telophase II  Chromosomes have reached opposite poles + cytokinesis Cytokinesis  Cytoplasm divides into separate cells Daughter cells are haploid and have genetic differences

14 Applying Your Knowledge A.When do sister chromatids separate? B.When does crossing-over occur? C.When do homologous pairs line up at the cell equator? 1.Prophase I 2.Metaphase I 3.Anaphase I 4.Metaphase II 5.Anaphase II

15 Sperm formation Equal divisions of cytoplasmEqual divisions of cytoplasm Four functional products per meiosisFour functional products per meiosis Egg formation Unequal divisions of cytoplasmUnequal divisions of cytoplasm Small polar bodies formedSmall polar bodies formed One functional product per meiosisOne functional product per meiosis Fertilization occurs after Meiosis I and stimulates Meiosis II

16 Comparing Mitosis and Meiosis MitosisMeiosis Cell type at start Cell type at end Are products identical? (Y/N) Number of cells produced Number of chromosome duplications Pairing of homologues (Y/N) Crossing-over (Y/N) Number of chromosome divisions

17 Comparing Mitosis and Meiosis MitosisMeiosis Cell type at start Cell type at end Are products identical? (Y/N) Number of cells produced Number of chromosome duplications Pairing of homologues (Y/N) Crossing-over (Y/N) Number of chromosome divisions Diploid Diploid Diploid Haploid Yes No NoYes No Yes 12


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