Biology 1201 Section 1 Cell Division Review Overview of Mitosis and Meiosis Mitosis Produces daughter cells with the 2n chromosome number Meiosis Occurs in specialized tissues produces cells with the 1n chromosome number Meiosis consists of two divisions Meiosis I separates homologous chromosomes Meiosis II separates sister chromatids Chromosome Complement Diploid chromosome number 2n Haploid chromosome number 1n Homologous chromosomes pairs of chromosomes of the same length and centromere position that posses genes coding for the same characters chromosomes of a cell size number and type Karyotypes are best viewed at metaphase of mitosis Karyotype method of organizing and visualizing the Interphase organelles Gap 1 G1 Increase in cell components increase in number of S phase Synthesis of DNA doubling of the genetic material Gap 2 G2 Centrioles replicate in animal cells structure for cytokinesis is put in place Mitosis Nuclear envelope fragments Microtubules of spindle invade the Prophase Nucleoli disappear chromatin condenses mitotic spindle forms from microtubules in cytoplasm centrosomes move away from each other Prometaphase nuclear region and interact with the chromosomes via the kinetochore Metaphase midplane of the spindle Kinetochores of sister chromatids are attached to opposite poles Anaphase Centrosomes at opposite poles Chromosomes arranged at the Sister chromatids separate and move toward the poles Nuclear envelope reforms spindle breaks down nucleoli reform Telophase chromatids become less densely coiled Cytokinesis Division of cytoplasm The mechanism differs between plant and animal cells because plants have a cell wall Control of the cell cycle G1 Checkpoint Check to see if DNA is damaged G2 Checkpoint Check to see if DNA is replicated properly M Checkpoint spindle assembly checkpoint check for alignment of chromosomes Meiosis Prophase I Spindle formation breakdown of nuclear envelope nucleoli disappear chromosomes condense Each chromosome consists of two chromatids from S phase of Interphase Homologous chromosome pairs lie next to one another Crossing over of chromatids between pairs chiasma formation occurs Metaphase I sister chromatids are attached to fibers going to the same pole Anaphase I Chromosome pairs align on equator of spindle Kinetochores of Homologous pairs of chromosomes separate Nuclear membrane may or may not reform cytokinesis may or Telophase I may not occur Meiosis II chromosome complement Sister chromatids are separated Cell division like mitosis but starting with the haploid Gamete formation in humans Spermatogenesis occurs in diploid reproductive tissues Primary Males spermatocyte undergoes meiosis I Secondary spermatocyte undergoes meiosis II The resulting spermatids mature into spermatozoa Females At about 3 months of age oogonia give rise to primary oocytes stopped in prophase I until ovulation Polar body formation gives rise to a large egg Mitochondria are inherited from the mother
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