Biology Final Exam Study Guide UNIT I variable measured o o In an observational test one has no control over the independent variable In an experiment there is an independent and dependent variable and one has control over the independent o Dependent variable value depends on that of another what is causing result what you Independent variable value does NOT depend on that of another Ex Effect flower color 0n attraction of bees Ind flower color Dep what result is Properties of Life order evolutionary adaptation response to the environment growth and development reproduction energy processing and regulation DNA allows for the properties of life to be maintained and passed from generation to generation Eukaryotic chromosomes are made of chromatin Chromatin is the complex of DNA and associated proteins that maintaining structure for gene activity and replication Each single chromosome contains one very long DNA molecule that carries several hundred to a few thousand genes the units that specify an organism s inherited traits Cell Cycle Interphase G1 S G2 and Mitotic M phase mitosis and cytokinesis Cell spends most of their time in the G1 phase o o DNA is replicated during the S phase o Cells divide in the Mitotic phase as well as the seperation of sister chromosomes Mitosis review diagrams in textbook genetically identical daughter cells development growth asexual reproduction o G2 two chromosomes form from replication from a single centrosome animal cells have two centrioles on each chromosome o Prophase chromatin coils nucleoli disappear chromosomes appear as sister chromatids joined at the centromere and along the arms by sister chromatid cohesion mitotic spindle forms centrosomes move away from each other o Prometaphase nuclear envelope fragments chromosomes are more condensed microtubules attach to kinetochore specialized protein on centromere non kinetochore microtubules interact with those from opposite pole o Metaphase longest stage centrosomes are on opposite poles of the cell chromosomes convene on the metaphase plate each kinetochore has microtubules from each pole connected to it o Anaphase shortest stage cohesion proteins are cleaved sister chromatids separate as individual chromosomes move towards the poles from microtubule shortening usually at kinetochore end cell lengthens as non kinetochore microtubules lengthen each end of the cell has equivalent and complete collections of chromosomes pulled apart o Telophase daughter nuclei form nuclear envelopes form chromosomes become less condensed division of cytoplasm beings Go back to normal o Cytokinesis Animal cell cleavage furrow pinches the cell in two Plant cell cell plate forms new cell wall that divides the two cells Certain molecules form checkpoints that control cell cycle G1 checkpoint if passed cell usually continues through rest of cycle G2 checkpoint lads to mitosis and M checkpoint start cycle over o o Cyclin synthesizes late in S phase and continues through G2 phase Cyclin combines with recycled cyclin dependent kinases cdk producing MPF Once enough accumulates cell passes G2 checkpoint starting mitosis o MPF promotes mitosis MPF activity peaks during metaphase o During anaphase cyclin component of MPF degrades terminating M phase o During G1 cyclin degrades Somatic chromosomes exist in homologous pairs in diploids 2n one from each parent Meiosis produces haploid daughter cells from diploid parents Many of the steps of meiosis closely resemble corresponding steps in mitosis Meiosis like mitosis is preceded by the replication of chromosomes However this single replication is followed by not one but two consecutive divisions called meiosis I and II These two divisions result in four daughter cells each with only half as many chromosomes as the parent cell Sexual life cycles vary in the timing of meiosis and fertilization Figure 13 6 perfectly explains this Plants and some species of algae exhibit a sexual life style called the alteration of Meiosis consists of two stages meiosis I and meiosis II the end product being four haploid cells each with a haploid set of genetically distinct chromosomes Review diagrams in textbook generations Sexual Reproduction Sister chromatids are separated in meiosis II o Homologous chromosomes are separated in meiosis I o o Prophase I chromosomes condense and homologs pair along their lengths aligned gene by gene Crossing over occurs while homologs are in synapsis while held together are still associated at the chiasmata After crossing over the homologs are still associated at the chiasmata due to sister chromatid cohesion Centrosomes move the spindle forms and the nuclear envelope breaks down Microtubules attach to the kinetochores o Metaphase I homologous chromosomes arrange on the metaphase plate Both of the chromatids of one homolog are attached to kinetochore microtubules from one pole those of the other homolog are attached to microtubules from the opposite pole o Anaphase I proteins responsible for sister chromatid cohesion along the chromatid arms breakdown allowing homologs to separate Homologs move toward opposite poles Sister chromatid cohesion along the poles persists at the centromere so chromatids move as a unit o Telophase I and Cytokinesis each half of the cell has a complete haploid set of replicated chromosomes composed of two sister chromatids Cytokinesis occurs simultaneously in the same way as during mitosis o Prophase II spindle apparatus forms Chromosomes move toward metaphase plate o Metaphase II chromosomes align on the metaphase plate Because of crossing over sister chromatids are not genetically identical o Anaphase II proteins holding sister chromatids together at centromere breakdown allowing chromatids to separate Chromatids move toward opposite poles as individual o Telophase II and Cytokinesis nuclei form chromosomes become less condensed and chromosomes cytokinesis occurs The random assortment of homologs into daughter cells and the process of crossing over result in genetically variable gametes The closer two loci are to each the less likely crossing over will occur Crossing over usually produces 9 3 3 1 ratio in a dihybrid cross Without crossing over if the gene loci are near each other it usually produces a 3 1 ration Law of Segregation two alleles in a pair segregate into different gametes during gamete formation Law of Independent Assortment each pair of alleles segregates independently of each other pair during gamete formation applies when
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