BIOL 3303 1st EditionExam # 3 Study Guide: Chapters 2-4CHAPTER 21. Describe the difference between prokaryotic and eukaryotic cell division.Recall:Prokaryotic:- Smaller cells- Lack internal membranes/ organelles- DNA is not isolated in a nuclear membrane- Circular chromosomeBoth:- Genetic material- Have ribosomesEukaryotic:- Bigger cells- System of membranes and well-organized organelles- Mitochondria/Chloroplasts- Nucleus-DNA (extra-nuclear DNA in mitochondria and chloroplasts)Prokaryotic cells divide by fission: the contents of the mother cell are divided between identical daughter cells. This is a version of __mitosis__.Eukaryotic cells divide by a more elaborate process involving divisions of the cell: meiosis, and mitosis and cytokinesis.Figure 1: From www.slideshare.net2. Identify the two types of cell division in eukaryotic cells and their respective functions.Mitosis: genetic material is divided equally and exactly to daughter cells.Meiosis: a mechanism of sexual reproduction that reduces the number of chromosomes by half; involves 2 cell divisions.3. Master the language including chromosome, sister chromatids, centromere, homologous chromosomes.Chromosome – discrete structure of a single molecule of DNA; can look like | or X in eukaryotes; prokaryotes have a single circular chromosome.Sister chromatid – one of 2 identical copies formed by the replication of a single chromosome.Centromere – the part of a chromosome that links sister chromatids; spindle fibers attach to the centromere (via the kinetochore) during mitosis to align and separate sisterchromatids.Homologous chromosomes – members of the same chromosome pair (same genes, different alleles).Heterologous chromosomes – members of different chromosome pairs4. Describe the stages of mitosis and the events that occur in each stage.[Interphase – DNA replication]Prophase – DNA packing (nucleosome>chromatin fibor>scaffold formationMetaphase – chromosomes align at metaphase plateAnaphase – sister chromatids separate, becoming daughter chromosomes, and move to opposite poles of the spindleTelophase – chromosomes decondense & nuclear membranes form[Cytokinesis occurs, resulting in 2 genetically identical daughter cells]5. Describe the stages of meiosis and the events that occur at each stage.[Interphase – DNA synthesis]Meiosis I:Prophase I – Leptonema (“thin threads”) chromosomes condenseZygonema (“paired threads”) homologues associate [synapsis]Pachynema (“thick threads”) exchanging material [crossing over]Diplonema (“two threads”) pairs separate slightly but remain in contact where crossed [chiasmata]Diakinesis (“movement through”) homologous pairs move to central plane of cell, perpendicular to axis of spindle apparatusMetaphase I – homologous pairs align at metaphase plateAnaphase I – homologous pairs separate to opposite polesTelophase I – chromosome movement is completed and new nuclei form[Cytokinesis occurs, resulting in 2 diploid cells]Meiosis II: Prophase II – chromosomes, ea. With 2 sister chromatids, condenseMetaphase II – chromosomes align at metaphase plateAnaphase II – sister chromatids separate, becoming daughter chromosomes, and move to opposite poles of the spindleTelophase II – chromosomes decondense and nuclear membranes form[Cytokinesis occurs, resulting in 4 haploid cells]Figure 2: From Principles of Genetics, 4/e, © 2006 John Wiley & Sons6. Count the number of chromosomes & chromatids at different stages of cell division/ compare and contrast between mitosis & meiosis in terms of mechanisms, events, andconsequences.Figure 3: From Principles of Genetics, 4/e, © 2006 John Wiley & Sons Ex: mitosis in humans2n = 46 chromosomesDNA REPLICATION2n = 46 chromosomesMITOSIS2n = 46 chromosomes2c = 46 chromatidsDNA REPLICATION4c = 92 chromatidsMITOSIS2c = 46 chromatids Ex: meiosis in humans2n = 46 chromosomesDNA REPLICATION2n = 46 chromosomesMEIOSIS In = 23 chromosomesMEIOSIS IIn = 23 chromosomes2c = 46 chromatidsDNA REPLICATION4c = 92 chromatidsMEIOSIS I2c = 46 chromatidsMEIOSIS IIc = 23 chromatids7. Specifically, when do the following events happen? (synapsis, crossing over, visualization of chiasmata, segregation of homologous chromosomes and segregation of sister chromatids)Synapsis: Meiosis I, Prophase I, ZygonemaCrossing over: Meiosis I, Prophase I, PachynemaVisualization of chiasmata: Meiosis I, Prophase I, DiplonemaSegregation of homologues: Meiosis I, Telophase ISegregation of sister chromatids: Meiosis II, Telophase II OR Mitosis, Telophase8. Describe what the cohesion complex and the synaptonema complex are and predict what happens if an error occurs.Cohesion complex – protein complex that regulates the separation of sister chromatids during cell divisionSynaptomena complex – protein structure between pairing chromosomes (homologues),consisting of 3 rods: 2 lateral elements + 1 central element, connected by ladder-like rungs9. Explain the meaning of genetic variation and how sexual reproduction differs from asexual reproduction in introducing genetic variation.In contrast to asexually reproducing organisms, who produce identical copies of their cells, sexually reproducing organisms divide their genetic material more complexly. During meiosis I (a mechanism of sexual reproduction), homologous chromosomes exchange material by crossing over during synapsis, creating countless different possible combinations of genes. Additionally, random disjunction of homologues can occur, causing daughter cells to be even less similar.Figure 4: Oogenesis and spermatogenesis in mammals. From Principles of Genetics, 4/e, © 2006 John Wiley & Sons10. Explain what a model system is and name some common ones. Understand the advantages and disadvantages of each model system and evaluate when each system should be used.Model research organisms, or model systems, are those that are well-suited for controlled experimentation in laboratories or field plots. Examples include: Eschericia coli (bacterium)Advantages: single circular chromosome, easy to manipulate; simple mechanismsSaccharomyces cerevisiae (baker’s yeast)Advantages: eukaryotic cells; sexual reproduction; cheap & easy to growDrosophila melanogaster (fruit fly)Advantages: multi-cellular; more complex cellular processes, i.e., cell differentiation; short life span; easily cultured; screening for mutantsCaenorhabditis elegans (round worm)Advantages: animal development – transparent; self-fertilizing