Lecture 1 BIO 311D 1st Edition Outline of Current Lecture I Vocabulary II Stages of Meiosis III A Comparison of Meiosis and Mitosis IV Characteristics Unique to Meiosis V Genetic Variation Contributes to Evolution Current Lecture Vocabulary 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 meiosis The Stages of Meiosis 1 Interphase Chromosomes duplicate 2 Meiosis I Homologous chromosomes separate a Prophase I Chromosomes condense homologous chromosomes pair up synapsis and crossing over occurs b Metaphase I Tetrads line at metaphase plate microtubules attach to kinetochores c Anaphase I Pairs of homologous chromosomes separate and move toward pole by spindle apparatus d Telophase I Cytokinesis Cleavage furrow divides the cell into two 3 Meiosis II Sister chromatids separate a Prophase II Spindle apparatus forms b 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 poles d Telophase II Cytokinesis Nuclei form and chromosomes decondense Each daughter cell is genetically different from the others e Anaphase II Sister chromatids separate and move towards opposite poles f Telophase II Cytokinesis Nuclei form and chromosomes decondense Each daughter cell is genetically different from the others A 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 DNA Replication Number of Divisions Synapsis of Chromosomes Number of Daughter Cells Role in the Animal Body Mitosis Interphase One None Two Identical Growth Repair Meiosis Interphase Two Prophase I Four Unique Produces Gametes Characteristics Unique to Meiosis all occur in Meiosis I 1 Prophase I Synapsis and crossing over occurs 2 Metaphase I Tetrads paired homologous chromosomes line up at the metaphase plate 3 Anaphase I Homologous chromosomes separate instead of sister chromatids Genetic 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 I 2 Crossing over Produces recombinant chromosomes during prophase I combines DNA from two parents 3 Random fertilization
View Full Document
Unlocking...