LECTURE 16 Mitosis Binary Fission chromosomes replicate divides two identical cells Key Roles of Mitosis development growth repair tissue renewal asexual reproduction Interphase period of cell growth when cell cannot divide genetic information is being accessed by cell from the chromosomes DNA molecules unspooled Chromosomes not visible microscopically Cell Cycle S phase DNA SYNTHESIS G1 G2 M Mitosis Chromatid replicated chromosome strand Sister Chromatids identical chromosome strands they separate during mitosis to form independent chromosomes Prophase chromosomes condense Prometaphase nuclear envelope breaks etc Steps of Mitosis Metaphase chrosomomes migrate to the middle of cell Anaphase sister chromatids separate Telophase nuclear envelope reforms Control of Cell Replication can be controlled by intrinsic and extrinsic factors cell cycle checkpoint is critical step in regulating cell cycle tumor suppressors are regulatory proteins that can cause a cell to remain in G1 phase Cancer out of control cell division all cancers derive from cells in which cell cycle checkpoints have failed most cancers result from multiple defects in cell cycle regulation each cancer is caused by a unique combination of errors accumulated via mutation mistakes in DNA replication the more divisions a cell lineage undergoes the more mutations it accumulates Tumor one or more cells divides uncontrollably o Benign tumors are noninvasive o Malignant tumors are invasive and can spread throughout the body via blood or lymph and initiate new tumors Each tumor had a different pattern of mutations in research most had never been found mutated before Why we get cancer p 53 tumor suppressor gene BRCA1 and BRCA2 are associated with increased fertility o Mismatches to modernity ex widespread use of birth control o More menstrual cycles with birthcontrol and since breast tissue differentiates and multiplies theres more opportunity for mutations o Associated with risk of breast cancer decreased risk of ovarian cancer LECTURE 17 Big Picture of Genetics Genetic variation is critical for evolution to occur Factors that generate genetic variation o Mutation o Recombination crossing over Sexual reproduction generates genetic diversity Binary Fission 2 genetically identical cells only in bacteria archaea 2 genetically identical daughter cells only in Eukaryotes only in somatic cells Mitosis Meiosis 4 daughter cells genetically different daughter cells two consecutive cell divisions 4 haploid daughter cells only in germ cells located in the gonads testes ovaries and eukaryotes daughter cells have half as many chromosomes as the parent cell occurs prior to the formation of eggs and sperm reason you only share 50 of your genome with parents siblings offspring Asexual reproduction one parent produces genetically identical offspring widespread among prokaryotes and unicellular eukaryotes widespread among prokaryotes protozoa plants also in minority of invertebrate and lower vertebrate animal lineages Can be facultative alternately sexual or asexual or obligate strictly asexual Advantages o Don t need a mate o Don t need to expend time energy or resources to attract a mate o Fewer risks from predators o Fewer risks of STDs o Lead to faster population increases Disadvantages o Little genetic variation for evolution to act upon o No way to get rid of deleterious mutations Sexual two indivudals combine genetic information and produce offspring that are genetically different So why RED QUEEN HYPOTHESIS sex produces genetic variation genetically diverse offspring MAY be more likely to surivive diseases parasites therefore more likely to persist in changing enviroments Meiosis sex generate genetic variation crossing over independent assortment o both of the above occur in the 1st cycle of meiosis random fertilization o this occurs after meiosis Crossing Over produces recombinant chromosomes that carry genes derived from two different parents homologous pairs of duplicated chromosomes are aligned to form tetrads produces recombinant chromosomes Independent Assortment each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs Random Fertilization adds to genetic variation STEPS OF MEIOSIS I Interphase Prophase I o homologous chromosomes come together exchange parts o Crossing over recombination Metaphase I o Homologous chromosomes line up INDEPENDENTLY adds to random in center of cell INDEPENDENT ASSORTMENT Anaphase I o Homologous chromosomes split apart STEPS OF MEIOSIS II Prophase Metaphase II o Chromosomes line up in the middle of the cell Anaphase II o Sister chromatids separate 2 n number of possible combinations N being the of traits NO REPLICATION OF CHROMOSOMES OCCURES BETWEEN M1 and M2