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Announcements

Announcements. ● Tutoring Center SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30, Th 8-12, 6-7; F 8-9 ● MasteringBiology Assignment due Tuesday 5/3 ● Bring you textbooks to Lab this week. Cellular Reproduction. Cell division.

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Announcements

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  1. Announcements ● Tutoring Center SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30, Th 8-12, 6-7; F 8-9 ● MasteringBiology Assignment due Tuesday 5/3 ● Bring you textbooks to Lab this week

  2. Cellular Reproduction Cell division Functions of cell division: *reproduction *growth and development *repair

  3. Cellular Reproduction • In asexual reproduction: • Single-celled organisms reproduce by simple cell division • There is no fertilization of an egg by a sperm FUNCTIONS OF CELL DIVISION Asexual Reproduction LM Sea stars African Violet Amoeba

  4. Cellular Reproduction • Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

  5. Eukaryotic Chromosomes LM Chromosomes

  6. Eukaryotic Chromosomes DNA double helix Histones • The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding. • Histones are proteins used to package DNA in eukaryotes. • Nucleosomes consist of DNA wound around histone molecules. “Beads on a string” TEM Nucleosome Tight helical fiber Looped domains Duplicated chromosomes (sister chromatids) TEM Centromere

  7. Chromosome Structure Chromosome Centromere Sister Chromatids

  8. The Cell Cycle S phase (DNA synthesis; chromosome duplication) • The cell cycle consists of two distinct phases • Interphase • Mitotic phase Interphase (90% of time) G1 G2 Mitotic phase (M) (10% of time) Mitosis Cytokinesis

  9. Interphase INTERPHASE Centrosomes (with centriole pairs) Interphase Chromatin • G1: Metabolism and growth • End of G1: Cell signaled to divide • S (synthesis): DNA is duplicated • G2: Cell forms chromosomes, completes preparations for cell and nuclear division Nuclear envelope Plasma membrane LM

  10. Prophase PROPHASE Fragments of nuclear envelope Early mitotic spindle Centrosome Centromere Chromosome, consisting of two sister chromatids Spindle microtubules Figure 8.7.a

  11. Metaphase, Anaphase, Telophase METAPHASE ANAPHASE TELOPHASE Nuclear envelope forming Cleavage furrow Daughter chromosomes Spindle

  12. Cytokinesis Animal cells Plant cells

  13. Meiosis • Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

  14. Meiosis Homologous chromosomes separate. Chromosomes duplicate. Sister chromatids separate. Duplicated pair of homologous chromosomes Pair of homologous chromosomes in diploid parent cell Sister chromatids MEIOSIS II MEIOSIS I INTERPHASE BEFORE MEIOSIS

  15. Meiosis MEIOSIS I: INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Microtubules attached to chromosome Sister chromatids remain attached Centrosomes (with centriole pairs) Sites of crossing over Spindle Sister chromatids Nuclear envelope Centromere Pair of homologous chromosomes Chromatin Homologous chromosomes pair up and exchange segments. Pairs of homologous chromosomes split up. Pairs of homologous chromosomes line up. Chromosomes duplicate.

  16. Meiosis MEIOSIS II: SISTER CHROMATIDS SEPARATE TELOPHASE II AND CYTOKINESIS TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavage furrow Sister chromatids separate Haploid daughter cells forming Two haploid cells form; chromosomes are still doubled. During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes.

  17. Meiosis Cross over: How do we account for genetic variation? *Independent assortment *Crossing over *Random fertilization Independent Assortment:

  18. Mitosis and Meiosis

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