BSC 2011 Unit II Study Guide1. A duplicated chromosome is one that was replicated during the “S” phase only ! because a decision was made for the chromosome to divide. 2. Cell Cycle ! Refers to cell growth and mitotic cell division Steps / Stages:! 1. 2 new daughter cells are created ! 2. Go to “G1” phase where a new cell grows! 3. Before entering “S” phase a decision is made to either stay and perform ! ! cellular activities or to divide! 4. “S” phase - chromosome replication! 5. “G2” phase - cell prepares to divide! 6. “M” phase - cell divides by mitosis and cytokinesis into 2 daughter cells (each ! ! with original number of chromosomes) 3. Cells/organisms need to regulate the cell cycle because it’s crucial for the survival of a cell, including the detection and repair of genetic damage and prevention of uncontrolled cell division. 4. Cell regulates the cell cycle through the 3 main checkpoints. Molecular signals in cytoplasm regulate cell cycle. ! - “G1” checkpoint: cell cycle pauses (cell “hangs out” doing its job in “G0”) if ! ! directed to do so by signals or signals direct the cell to pass the ! ! checkpoint and enter “S” phase or to undergo apoptosis. !! - “G2” checkpoint: signals prepare cell to enter “M” phase if it’s all “ok”! During “G0” = apoptosis or repair happens here!The MPF signal puts the cell through the “G2” checkpoint and initiates mitosis!!Cyclin and Cdk together (later degraded after mitosis begins)! ! ! - Must be in high concentration for Cdk to bind 5. Purpose for mitotic cell divisions: division of the nucleus that preserves the parental chromosome number in both daughter cells. some of its functions include: asexual reproduction, development, tissue growth, and repair Chromosomes:! 4! Prophase - centrosomes move to opposite poles; spindle fibers start to ! ! form; nucleolus disintegrates; chromatin condenses forming distinct ! ! chromosomes! 4 ! Pro-Metaphase - kinetochore appears in centromere and attaches sister ! ! chromatids to the spindle fibers ! 4! Metaphase - chromosomes align in a single file along the M-plate; sister ! ! chromatids face opposite poles !! 8! Anaphase - sister chromatids split from each other; each is a distinct ! ! chromosome! 4 ea.! Telophase & Cytokinesis - cell membrane pinches in at cleavage furrow; 2 ! ! daughter cells result; each with the same number of chromosomes as ! ! parent cell; each with identical DNA as parent cell ! ! ! Telophase: spindle disassembles; nuclear membrane reforms ! ! ! nuclear division complete! ! ! Cytokinesis: cytoplasmic division complete6. Cancer & Cell Cycle - cancer results from errors in cell cycle control such as a proto-oncogene mutation, where you get uncontrolled cell growth (cancer); also an error in stimulating pathways which result in uncontrolled cell growth due to proteins that stimulate cell growth; a tumor suppressing gene mutation causes cancer as well since this gene inhibits cell division and mutation will cause uncontrolled cell growth. 7. Somatic Cells - diploid (2n)- 2n = 2 sets (maternal and paternal) of chromosomes- body cells: muscle, nerve, skin, and liver - formed through homologous chromosome pairs (1 from maternal, 1 from paternal)Germ Cells (Gametes)- haploid (n)- each set contains just 1 chromosome from each pair for a particular species - sex cells: egg/sperm cells 8. Karyotype: orderly way of displaying the number and types of chromosomes in a cell; it displays already replicated chromosomes (homologous pairs); it shows the different kinds of genes and their chromosomal number; reveals autosome and sex chromosomes; useful to detect abnormalities in chromosome number and size; detect gender 9. Chromosomes exist in pairs: 2 sets in diploid somatic cells! ! ! ! Maternal and Paternal contributions ! Similarity: same kind of gene; alleles may be the same! Difference: alleles may be different for the same gene! Gene = color ! ! ! Allele = purple, white10. Diploid chromosome number - 2n [somatic cells] Haploid chromosome number - n (half of diploid) [sex cells / germ cells]11. Purpose for meiotic cell division: for a diploid cell to divide to produce haploid daughter cells (gametes) with half the chromosome number! Prophase I - crossing over occurs at chiasma between homologous ! chromosomes; they pair up! Metaphase I - tetrads formed line up on M-plate! Anaphase I - homologous chromosomes separate ! Telophase I & Cytokinesis - result in 2 haploid cells; still attached Meiosis II - same as mitosis, except 4 haploid cells formed and are genetically different due to crossing over (trading of alleles)12. MitosisMeiosis Chromosomes align at M-plate Tetrads form in Prophase ISister chromatids separate in Anaphase Tetrads align at M-plateDiploid parent cell = 2 diploid daughter cellsHomologous chromosomes separate during Anaphase I; sister chromatids remain together until Anaphase IIMitosisMeiosis Daughter cells are identical to each other and to parent Diploid parent = 4 haploid daughter cells (genetically different)Independent Assortment 13. Meiosis contributes to genetic variation among diploid organisms through crossing over and independent assortment. This is important for the production of genetically different gametes and thus genetically different offspring.14. Mendel’s intention was to study inheritance. He used pea plants that can both self and cross fertilize, produce many offspring, relatively short generation time. Made sure his starting plants were true breeding purple (homologous dominant) and white (homozygous recessive). Cut stamens off in purple flowers, transferring pollen from white flowers to egg-bearing carpel of purple flower. Pollinated carpel matured into pod, and planted seeds from pods. Resulted in all purple flowers [F1 generation]. [F2 generation] Mendel self fertilized the F1 plants. 15. Trait - a characteristic such as flower color, flower position, seed color/shape, pod color/shape, and stem length. ! Traits are passed from on from one generation to the next by each parents ! contribution of 1 allele for each trait gene (via gamete)16. F1 = 1st generation offspring F2 = 2nd generation offspring P = P generation (true breeding parents)17. Genes - a specific locus on a chromosome that determines a heritable characteristic Alleles - different forms of the same gene due to slightly different DNA sequences 18. Gametes must be haploid because in
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