Announcements SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30, ● 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 1

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

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 Amoeba Sea stars African Violet 3

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

Eukaryotic Chromosomes LM 5

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 6

Chromosome Structure Chromosome Centromere Sister Chromatids 7

chromosome duplication) 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

Interphase G1: Metabolism and growth Centrosomes (with centriole pairs) Interphase 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 Chromatin Nuclear envelope Plasma membrane LM

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

Metaphase, Anaphase, Telophase Nuclear envelope forming Cleavage furrow Spindle Daughter chromosomes

Cytokinesis Animal cells Plant cells

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

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

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

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

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

Mitosis and Meiosis 18