Zoology 101: Animal Biology Last Lecture Outline Lecture 15 1. Normal Cells • Cell cycle • Cell division • Properties of normal cells • how external signal regulates cell division2. Cancer cells• Properties • Cell division3. How proto-oncogens become oncogens4. Proteins that inhibit cell division Current Lecture 1. Finish up on cancer2. Meiosis3. Sexual ReproductionFinish up on Cancer• In cancers, telomerase is expressed and cell becomes immortal• Stop expression mRNA level using RNA inhibition (RNAi) ◦ Makes hybrid molecule: cannot be translated; complimentary to telomerase • Traditional chemo: chemicals kill dividing cells◦ Stop mitosis◦ Taxol: prevents kinetochore MT's from shortening • Radiation therapy: damages DNA◦ Cell dies • Usually more than one mutation → cancer → benign → Malignant → metastasis Meiosis • Prokaryotes reproduce by binary fission• Some eukaryotes can reproduce by mitosis/cytokinesis ◦ Asexual reproduction: offspring is identical to parten ◦ Sexual reproduction: offspring is not identical to parents • Life cycle of a sexual cell◦ gamete formation (meiosis)◦ Fertilization- union of gametes ◦ growth (mitosis) and development • Meiosis: 2n cell has 4 1n Cells• Daughter cells not identical to parent or each other • Sex chromosomes determine sex while autosomes are non sex chromosome genes • For homologous genes, at a given position it is the same gene (eye color locus)• many have different alleles (alternative versions of a gene) • Only go through the cycle once• Has same cycle as mitosis (G1,S, G2) but different features • Prophase 1: ◦ Chromosomes condense ◦ Nuclear envelope fragments◦ Centrosomes migrate to opposite poles ◦ MEIOTIC spindle form ◦ Synapsis occurs- pairing up of homologous chromosomes ◦ Synatonemal complex- protein lattice between homologous chromosomes ◦ Cohesions connect sister chromatids along the length ◦ Crossing over occurs- exchange of genetic material▪ between non sister chromatids • Non-recombinant chromatids (not crossed)• Recombinant chromatids • Metaphase 1:◦ Homologous pairs align on the metaphase plate via random alignment (independent assortment)• Anaphase 1: (separation)◦ Kinetochore Mts shorten ◦ Synaptonemal complex degrades ◦ Homologous chromosomes separate- move to opposite sides of the cell ◦ sister chromatids stay attached ◦ non-kinetochore mts lengthen → cell elongates • Telophase/Cytokinesis:◦ Each half cell has complete haploid (n) set of replicated chromosomes ◦ Each chromosome consists of 2 sister chromatids ◦ Some species:▪ Chromosomes decondense ▪ nuclear envelope reforms◦ No DNA replication occurs ◦ Both Cells enter Meiosis II • Prophase II ◦ Synapsis and crossing over don't occur◦ Like Mitosis • Metaphase II◦ Chromosomes aligned on metaphase plate • Anaphase II◦ Sister chromatids move to opposite pole of the cell• Telophase II◦ Chromosomes decondense◦ nuclei reform ◦ 4 haploid daughter cells◦ All different Sexual Reproduction • gametes are variable• 3 genetic variations ◦ 1. Random alignment of chromosomes on metaphase plate (8.4 million) ◦ 2. Crossing over (>8.4 million)◦ 3. Fertilization (over 70 trillion
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