Lecture 1 BIO 311D 1st EditionOutline of Current LectureI. VocabularyII. Stages of MeiosisIII. A Comparison of Meiosis and MitosisIV. Characteristics Unique to MeiosisV. Genetic Variation Contributes to EvolutionCurrent LectureVocabulary:- Gametes: Reproductive cells and are haploid cells (ex. Sperm and eggs)o Gametes are the only haploid cells in humans- Locus: A specific location on a chromosome- Somatic Cells: Body cells/any other cell than a gamete- Karyotype: Ordered display of chromosome pairs in a cell- Homologous chromosomes: 2 chromosomes, one chromosome from each parent- Tetrads: Four chromosomes in meiosis I- Diploid Cell (2n): Contains two sets of chromosomes (ex. Humans 2n=46)o Only diploid cells undergo meiosisThe Stages of Meiosis:1. Interphase: Chromosomes duplicate2. Meiosis I: Homologous chromosomes separatea. Prophase I: Chromosomes condense, homologous chromosomes pair up (synapsis), and crossing over occursb. Metaphase I: Tetrads line at metaphase plate, microtubules attach to kinetochoresc. Anaphase I: Pairs of homologous chromosomes separate and move toward pole by spindle apparatusd. Telophase I/Cytokinesis: Cleavage furrow divides the cell into two3. Meiosis II: Sister chromatids separatea. Prophase II: Spindle apparatus formsb. Metaphase II: Sister chromatids (due to crossing over, sister chromatids are no longer identical) align at the metaphase plate and microtubules attach to kinetochores.c. Anaphase II: Sister chromatids separate and move towards opposite polesd. Telophase II/Cytokinesis: Nuclei form and chromosomes decondense*Each daughter cell is genetically different from the otherse. Anaphase II: Sister chromatids separate and move towards opposite polesf. Telophase II/Cytokinesis: Nuclei form and chromosomes decondense*Each daughter cell is genetically different from the othersA Comparison of Mitosis and Meiosis:- Mitosis: Produces cells identical to parent cells- Meiosis: Reduces the number of chromosome sets from 2 (diploid) to 1 (haploid)Property Mitosis MeiosisDNA Replication Interphase InterphaseNumber of Divisions One TwoSynapsis of Chromosomes None Prophase INumber of Daughter Cells Two (Identical) Four (Unique)Role in the Animal Body Growth, Repair Produces GametesCharacteristics Unique to Meiosis (all occur in Meiosis I):1. Prophase I: Synapsis and crossing over occurs2. Metaphase I: Tetrads (paired homologous chromosomes) line up at the metaphase plate3. Anaphase I: Homologous chromosomes separate instead of sister chromatidsGenetic Variation Contributes to Evolution:- Mutations are the source of genetic diversity- Three mechanisms that contribute to genetic variation:1. Independent assortment of chromosomes- Homologous pairs randomly orient at metaphase I2. Crossing over- Produces recombinant chromosomes during prophase I (combines DNA from two parents)3. Random
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