Chapter 7 - 204-325 1 Summary of the Last Lecture Genetic...

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Unformatted text preview: 204-325 1 Summary of the Last Lecture Genetic recombinants have allele combinations different from parental allele combinations. Recombination is the result either of independent assortment or of crossover. Crossover is the reciprocal exchanges between homologous chromosomes at the four chromatid stage of meiosis. One genetic map unit (mu or cM) is the interval in which 1% crossover occurs. Gene mapping crosses measure recombination frequencies, which are used to estimate the crossover frequencies of genes within 7 mu. 2 Today's Topics 1. Tetrad Analysis in Haploid Eukaryotes Linear (ordered) Tetrad Analysis for Gene-Centromere Mapping Random-Spore Analysis for Gene Mapping (unordered tetrads) 2. Mitotic Recombination 3. Mapping Human Genes 3 Topic 1 Tetrad Analysis in Haploid Eukaryotes 4 Tetrad Exists only in Meiosis 1 Tetrad: products of a Single Meiosis 5 Different Life Cycles of Animals, Plants and Fungi anther ovule dead gp=gametophyte 6 Many Ways of Sex Determination Genetic Sex Determination XY System: XY (or XO) , XX Y determination: mammal (including human) X to autosome set ratio: fly, worm, some plant WZ System: ZZ , WZ bird, butterfly, moth, some fish Diploidity / Haplodity: Diploid , Haploid ant, bee, wasp yeast mating type a and Neurospora A and a bacteria F+ and FChromosome Difference (Genotypic) Genic determination (alleles), Syngamous Mating Environmental Sex Determination One turtle species: 320C , 280C 7 Life Cycle of the Yeast Saccharomyces cerevisiae Unordered Tetrad 8 Life Cycle of Neurospora crassa Ordered (Linear) Tetrad 9 Two Kinds of Asci from a Tetrad Unordered Tetrad Tetrad Ordered Tetrad 10 Linear (Ordered) Tetrad Formation in Neurospora 11 Determination of Gene-Centromere Distance in Neurospora First-division segregation occurs when the two alleles of a gene separate from each other during meiosis I. Second-division segregation occurs when the two alleles of a gene separate from each other during meiosis II. First or Second-division segregation can be determined by looking at linear tetrads. 12 First-division Segregation in Ordered Tetrads A separated from a in Meiosis 1 (A:a) Parental chromosome (no recombination) 13 Second-division Segregations in Ordered Tetrads A separated from a in Meiosis 2 Parental chromosome (no recombination) Recombination between gene and centromere 14 Second-division Segregations (Cont.) A separated from a in Meiosis 2 Parental chromosome (no recombination) Recombination between gene and centromere 15 Calculating Gene-Centromere Distance in Ordered Tetrads The map distance between a gene and its centromere is determined by the number of asci that show second-division segregation. Gene-Centromere = Recombinant Frequency distance = % second-division tetrads 2 16 Unordered Tetrad Analysis: Three Types of Tetrads 17 Tetrad Types of Two Genes on Different Chromosomes PD = NPD 18 Tetrad Types of Two Genes on the Same Chromosome 19 Tetrad Types of Two Genes on the Same Chromosome 1:1:1:1 20 Calculating Map Distance in Ordered or Unordered Tetrads Basic mapping formula: number of recombinants X 100 total number of progeny Use types of tetrads (PD, NPD, T), the formula becomes: T + NPD X 100 total tetrads 21 Example (Question 7.6) leu rib+ 110 leu rib+ leu leu leu+ leu+ 45 rib rib+ rib+ rib X leu+ rib 6 leu+ leu leu leu+ rib+ rib rib rib+ leu leu+ leu+ leu 39 rib+ rib rib+ rib leu+ rib leu rib+ leu+ rib PD T NPD T (45 + 39) + 6 110+45+6+39 X 100 = 24 mu 22 Animation: Tetrad Analysis 23 Topic 2 Mitotic Recombination 24 Mosaic Phenotypes due to Mitotic Recombination y + sn y sn + 25 Mitotic Recombination Leads to Homozygosity of Distal Genes rare! rare! Single Spot Twin Spot 26 Diploid Aspergillus Colonies Some diploids from yellow w paba y sector are + paba y paba- in or phenotype, + + y w paba y thus y and paba are on Mitotic Recombination the same chromosome + + arm and the paba y order is centromere paba - y Diploids from white sector are paba+ in phenotype, thus w is on a separate chromosome (or chromosome arm) w w + + paba y Mitotic Recombination w + w + + paba 27 + y Mitotic Crossover 1 Produces Yellow Sector that is paba- Crossover 1: Yellow sector will not survive unless paba is provided 28 Mitotic Crossover 2 Produces Yellow Sector that is paba+ Crossover 2: Yellow sector does not require paba for survival 29 Mapping by Mitotic Crossover crossover 2: y- paba+ region 2 + paba region 1 crossover 1: y- paba- + y Ratio of crossover 1 and crossover 2 equals ratio of map units of region 1 and region 2 30 Topic 3 Mapping Human Genes 31 Mapping Human Genes by Pedigree Analysis Genetic Map 32 High Density Microsatellite Molecular Map of Human Genome Genetic Map 33 Physical mapping by Fluorescent in situ Hybridization (FISH) Physical Map 34 Physical Mapping by Making Radiation Hybrids (RH) Physical Map 35 Summary Ordered Tetrads in haploid eukaryotes can be used to map the distance between a gene and its centromere. Ordered and unordered Tetrads in haploid eukaryotes can be used to map the distance between two genes. Rare mitotic recombination can result in mutant patches of somatic cells. Mitotic recombination can be used to map genes. Pedigree analysis, molecular markers, fluorescent in situ hybridization, and radiation hybrid are used to map human genes. 36 ...
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This note was uploaded on 04/29/2008 for the course BIO SCI 325 taught by Professor Zang during the Spring '08 term at Wisconsin Milwaukee.

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