Review Sheet Lectures 30-39

Review Sheet Lectures 30-39 - I. Lectures 34 II. III. I....

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I. Lectures 34 II. III. I. Meiosis= reduction division; 2 nuclear divisions without S-phase in between (no DNA replication) IV. - Meiosis I= 2n4x4c 1n2x2c V. Tetrads separate into meiotic chromosomes Primary Meiocytes formed - Meiosis II= 1n2x2c 1n1x1c Meiotic chromosomes separate into individual chromatids Secondary Meiocytes formed *FOUR HAPLOID GAMETES result II. Amphitelic vs Syntelic Orientation Amphitelic = sister chromatids face opposite poles; they split up and move in opposite directions 46 groups of paired chromatids Syntelic = sister chromatids remain together, both face the same pole 23 groups of paired chromosomes at metaphase plate (23 tetrads) Tetrad/Bivalent = two chromosomes joined together (4 chromatids) III. Meiotic Prophase I 1. Leptotene a. Compacted chromosomes become visible (46 are present) b. Because cell is still 2n4x4c, way more DNA than in meiotic prophase II c. No bivalents present 2. Zygotene a. Synapsis= process that pairs homologous chromosomes bivalents forming i. Synaptonemal complexes = hold homologous chromosomes together (Cohesin= holds sister chromatids together) b. Nuclear envelope still intact 3. Pachytene a. Synapsis ends, synaptonemal complexes fully formed (tetrads fully formed) b. Genetic recombination begins 4. Diplotene a. Synaptonemal complexes break down; hom chrom now held together by chiasmata i. Chiasma = covalent attachment at crossover point between non-sister chromatids site of genetic recombination *Some notes on recombination: -Recombination= exchange of arms of non-sister chromatids, first seen in pachytene, goal is to increase genetic diversity -Crossover between sister chromatids would not change anything because they are identical -Recombination is not considered a mutation because it does not change the DNA sequence of a gene 5. Diakinesis a. Meiotic spindle forms and bivalents are ready for metaphase I b. Chiasmata continue holding homologous chromosomes together
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c. Nuclear envelope begins breaking down and spindle MT’s begin contacting chrom. Lecture 35 IV. Normal sources of Genetic Variability 1. Crossing over/ Recombination=Pachytene of Meiotic Prophase I 2. Independent Assortment of genetic traits= Anaphase I of Meiosis V. Other sources of Genetic Variability 1. Aneuploidy = wrong number of chromosomes -Can result from primary or secondary nondisjunction (chromosomes or chromatids don’t pull apart properly) -Autosomal polyploidy/monosomy -Sex chromosome polyploidy/monosomy 2. Genetic mutations -Mutation = a spontaneous change in a gene that alters it in a permanent fashion so that it causes heritable change 3. Other DNA modification: -Whole genome duplications, gene duplications, “Jumping genes”, viruses VI. Mitosis/Meiosis strategies 1. Gametic (Terminal)= used by multicellular animals and many protists a. Adult stage is diploid b. Meiosis only occurs in specialized sex cells c. Gametes= Oocytes (female) and Spermatocytes (male) differentiate into eggs and sperms 2. Zygotic (Initial)= used by fungi
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This note was uploaded on 09/30/2010 for the course BIO 201 taught by Professor Janicke during the Spring '08 term at SUNY Buffalo.

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Review Sheet Lectures 30-39 - I. Lectures 34 II. III. I....

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