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 variable Dependent variable: value depends on that of another, what is causing result, what you measured. 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
DNA is replicated during the S phase
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) G2: two chromosomes form from replication from a single centrosome (animal cells have two centrioles on each chromosome). 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. 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. 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. 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. Telophase: daughter nuclei form; nuclear envelopes form; chromosomes become less condensed; division of cytoplasm beings. (Go back to normal) 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) 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. MPF promotes mitosis. MPF activity peaks during metaphase.
During anaphase, cyclin component of MPF degrades, terminating M phase. 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...
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