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(a) Hydra

0.5 mm. Parent. Bud. (b) Redwoods. (a) Hydra. 5 µm. Pair of homologous replicated chromosomes. Centromere. Sister chromatids. Metaphase chromosome. Key. Maternal set of chromosomes ( n = 3). 2 n = 6. Paternal set of chromosomes ( n = 3). Two sister chromatids

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(a) Hydra

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  1. 0.5 mm Parent Bud (b) Redwoods (a) Hydra

  2. 5 µm Pair of homologous replicated chromosomes Centromere Sister chromatids Metaphase chromosome

  3. Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosome Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set)

  4. Key Haploid gametes (n = 23) Haploid (n) Egg (n) Diploid (2n) Sperm (n) MEIOSIS FERTILIZATION Testis Ovary Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

  5. Key Haploid (n) Haploid unicellular or multicellular organism Haploid multi- cellular organism (gametophyte) Diploid (2n) Gametes n n Mitosis Mitosis Mitosis Mitosis n n n n n n n n Spores n FERTILIZATION MEIOSIS n Gametes Gametes n MEIOSIS FERTILIZATION Zygote MEIOSIS FERTILIZATION 2n 2n 2n 2n Diploid multicellular organism Zygote Diploid multicellular organism (sporophyte) 2n Mitosis Mitosis Zygote (a) Animals (c) Most fungi and some protists (b) Plants and some algae

  6. Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes Meiosis I Homologous chromosomes separate 1 Haploid cells with replicated chromosomes Meiosis II Sister chromatids separate 2 Haploid cells with unreplicated chromosomes

  7. Telophase I and Cytokinesis Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II Metaphase I Prophase I Anaphase I Centrosome (with centriole pair) Sister chromatids remain attached Centromere (with kinetochore) Sister chromatids Chiasmata Spindle Metaphase plate Sister chromatids separate Haploid daughter cells forming Homologous chromosomes separate Cleavage furrow Homologous chromosomes Microtubule attached to kinetochore Fragments of nuclear envelope

  8. MITOSIS MEIOSIS MEIOSIS I Chiasma Parent cell Chromosome replication Chromosome replication Prophase I Prophase Homologous chromosome pair 2n = 6 Replicated chromosome Metaphase I Metaphase Anaphase I Anaphase Telophase Telophase I Haploid n = 3 Daughter cells of meiosis I MEIOSIS II 2n 2n Daughter cells of mitosis n n n n Daughter cells of meiosis II

  9. SUMMARY Mitosis Property Meiosis DNA replication Occurs during interphase before mitosis begins Occurs during interphase before meiosis I begins Number of divisions One, including prophase, metaphase, anaphase, and telophase Two, each including prophase, metaphase, anaphase, and telophase Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Synapsis of homologous chromosomes Does not occur Two, each diploid (2n) and genetically identical to the parent cell Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Number of daughter cells and genetic composition Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes Role in the animal body

  10. Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4

  11. Prophase I of meiosis Nonsister chromatids held together during synapsis Pair of homologs Chiasma Centromere TEM Anaphase I Anaphase II Daughter cells Recombinant chromosomes

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