Bios 208 1st EditionExam # 6 Study Guide I. Cell Cycle StagesA. The cell cycle consists ofB. Mitotic (M) phase (mitosis and cytokinesis)C. Interphase (cell growth and copying of chromosomes in preparation for cell division)D. Interphase (about 90% of the cell cycle) can be divided into sub-phasesa) G1 phase (“first gap”)b) S phase (“synthesis”)c) G2 phase (“second gap”)E. The cell grows during all three phases, but chromosomes are duplicated only during the S phaseF. Mitosis is conventionally divided into five phasesa) Prophaseb) Prometaphasec) Metaphased) Anaphasee) TelophaseG. Cytokinesis overlaps the latter stages of mitosisH. The Mitotic Spindlea) The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosisb) In animal cells, assembly of spindle microtubules begins in the centrosome, the microtubule organizing centerc) The centrosome replicates during interphase, forming two centrosomes that migrateto opposite ends of the cell during prophase and prometaphased) An aster (a radial array of short microtubules) extends from each centrosomee) The spindle includes the centrosomes, the spindle microtubules, and the astersII. MitosisI. Pro-metaphase and Metaphasea) During pro-metaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomesb) Kinetochores are protein complexes associated with centromeresc) At metaphase, the chromosomes are all lined up at the metaphase plate, an imaginary structure at the midway point between the spindle’s two polesJ. Anaphasea) In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cellb) The kinetochore contains motor proteins that “walk along” the microtubules, pulling the chromosomes.c) The microtubules shorten by depolymerizing at their kinetochore endsd) An analogy is climbing up a rope that is deteriorating underneath you! This can be seen by experiments marking the microtubules e) Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cellK. Telophasea) In telophase, genetically identical daughter nuclei form at opposite ends of the cellb) Cytokinesis (visible cell division) begins during anaphase or telophase and the spindle apparatus eventually disassembles.III. Cell Division A. Living organisms are distinguished by their ability to reproduce their own kindB. Genetics is the scientific study of heredity and variationC. Heredity is the transmission of traits from one generation to the nextD. Variation is demonstrated by the differences in appearance that offspring show from parents and siblingsE. Offspring acquire genes from parents by inheriting chromosomesF. In a literal sense, children do not inherit particular physical traits from their parentsG. It is genes that are actually inheritedH. Genes are the units of heredity, and are made up of segments of DNAI. Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs)J. Each gene has a specific location called a locus on a certain chromosomeK. Most DNA is packaged into chromosomesIV. Sexual Life Cycles (Haploid and Diploid stages)A. Human somatic cells (any cell other than a gamete) haveB. 23 pairs of chromosomesC. The two chromosomes in each pair are called homologous chromosomes, or homologsD. Chromosomes in a homologous pair are the same length and shape and carry genes controlling the same inherited charactersE. The sex chromosomes, which determine the sex of the individual, are called X and YF. Human females have a homologous pair of X chromosomes (XX)G. Human males have one X and one Y chromosomeH. The remaining 22 pairs of chromosomes are called autosomesI. Each pair of homologous chromosomes includes one chromosome from each parentJ. The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the fatherK. A diploid cell (2n) has two sets of chromosomesL. For humans, the diploid number is 46 (2n = 46)M. In a cell in which DNA synthesis has occurred, each chromosome is replicatedN. Each replicated chromosome consists of two identical sister chromatidsO. A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n)P. For humans, the haploid number is 23 (n = 23)V. MeiosisA. After chromosomes duplicate, two divisions followB. Meiosis I (reductional division): homologs pair up and separate, resulting in two haploid daughter cells with replicated chromosomesC. Meiosis II (equational division) sister chromatids separateD. The result is four haploid daughter cells with un-replicated ChromosomesE. Meiosis I is preceded by interphase, when the chromosomes are duplicated to form sister chromatidsF. The sister chromatids are genetically identical and joined at the centromereG. The single centrosome replicates, forming two centrosomesH. Division in meiosis I occurs in four phasesa) Prophase Ib) Metaphase Ic) Anaphase Id) Telophase I and cytokinesisI. Prophase Ia) Prophase I typically occupies more than 90% of the time required for meiosisb) Chromosomes begin to condensec) In synapsis, homologous chromosomes loosely pair up, aligned gene by gened) In crossing over, non-sister chromatids exchange DNA segmentse) Each pair of chromosomes forms a tetrad, a group off our chromatidsf) Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred J. Metaphase Ia) In metaphase I, tetrads line up at the metaphase plate, with one chromosome facing each poleb) Microtubules from one pole are attached to the kinetochore of one chromosome of each tetradc) Microtubules from the other pole are attached to the kinetochore of the other chromosomeK. Anaphase Ia) In anaphase I, pairs of homologous chromosomes separateb) One chromosome moves toward each pole, guided by the spindle apparatusc) Sister chromatids remain attached at the centromere and move as one unit toward the poleL. Telophase I and Cytokinesisa) In the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatidsb) Cytokinesis usually occurs simultaneously, forming two haploid daughter cellsc) In animal cells, a cleavage furrow forms; in plant cells, a cell plate formsd) No chromosome replication occurs between the end of meiosis I and the beginning of meiosis II because thee) Chromosomes are already replicatedM. Division in meiosis II also