Raunvísindadeild; Líffræðiskor Erfðafræði Verkleg Erfðafræði Sordaria Fimicola’s Ascuses Námsbraut: Raunvísindadeild; Líffræðiskor Námskeið: 09.51.35 Erfðafræði Nafn kennara: Ólafur S. Andrésson, Zophonías O. Jónsson, Sigríður H. Þorbjarnardóttir og Bryndís K. Gísladóttir. Vikudagur, hópur: Fimmtudagur, síðari kennslustund, Hópur 2 og 4. Tilraun framkvæmd: 30. október og 06. nóvember, 2003 Skýrsluskil til kennara: 13. nóvember, 2003 Skýrsluskil til stúdenta: Einkunn: Nöfn stúdenta: Bjarki Steinn Traustason, Egill Guðmundsson, J. Gabriel-Rios Kristjánsson, Marcella Manerba og Nicoletta Palmegiani. ________________________________ Bjarki Steinn Traustason ________________________________ J. Gabriel-Rios Kristjánsson ________________________________ Egill Guðmundsson ________________________________ Marcella Manerba ________________________________ Nicoletta Palmegiani Háskóli Íslands Raunvísindadeild; Líffræðiskor 7 Erfðafræði Sordaria Fimicola’s Ascuses Introduction: Sordaria fimicola is an ascomycetes related to Neurospora. Sordaria fimicola’s asuses, where meiosis progresses in, are examined, but they are many together in co called peritheca. When meiosis has concluded, the total of 4 spores have developed, but each nucleus, subsequently, undergoes mitosis, meaning, there is the total of 8 spores in each ascus, where two and two spores are identical if no mutation or gene conversion has occured. Two Sordaria-strains, one with dark spores (d+), and the other with light spores (d−), are cultured together on the same petri plate with mais agar. Specimens, perithecas, where obtained form where the tvo cultures meet, peripheral, on the petri plate, wherein one can assume that some of spores have intermixed. When separation in former cell division has occured, 4 dark spores are in the one half of the ascus, and 4 light spores are in the other (FIGURE 01 ■). But when separation in latter division takes place, because of interconversion between the d-gene and the centromere, identical spores pair, leading to one dark pair and one light pair located alternately in the ascus (FIGURE 01 ■). There are exception to these form of ascuses. One example is when ascuses contain equal number of dark spores end light spores, but the order of the spores indicates that separation has occured after meiosis. Also, ascuses can form, where the number of dark and light spores is unequal. The most prevalent ratio is then, 5d+:3d−, 3d+:5d−, 6d+:2d−, 2d+:6d−. One can explane these irregluar ascuses with the formation of heteroduplexes and during recombination, and with restoration because of heteroduplexes. FIGURE 01, DIFFERENT ORDER OF DARK (d+) AND LIGHT (d–) SPORES: 4d :4d 4d :4d 4d :4d 4d :4d AA 4d :4d 4d :4d 4d :4d 4d :4d 4d :4d 4d :4d 4d :4d 4d :4d BB CC A. Separation after division I., B. Schematic drawing from a microscope, C. Separa-tion after division II. □ Aims/Hypothesis: The Aim of this experiment, is to determine the distance between the d-gene and the centromere in the chromosome. Here, interpreting the distance in units of recombination, RU. Design and Methods: Háskóli Íslands Raunvísindadeild; Líffræðiskor Erfðafræði Reference to work sheets in manual booklet, for present exercise (p.29-30). Results: FIGURE 02, DIFFERENT TYPES OF ASCUSES: Type I 4d :4d Type II 4d :4d Type III 4d :4d Type IV 4d :4d Type V 4d :4d Type VI 4d :4d Information for this figure is interpreted in TABLE 01. □ TABLE 01, NUMBER FOR EACH TYPE OF ASCUS, GIVEN RESULTS: Number Type I Type II Number 52 60 25 18 20 25 Type III Type IV Type V Type VI TABLE 02, THE NUMBER OF ASCUSES Separation I. Separation II. Number § Σ 52 + 60 18 + 25 + 20 +25 112 88 dcentromere to d-gene = 22 RU * These numbers are given data, because the disired separation didn’t occur. *Formula used for the calculationsn of d, is described in Formula 01. § The distance between the centromere and the d-gene is 22 RU. FORMULA 01; DISTANCE BETWEEN THE CENTROMERE AND THE d-GENE: General Formula: d = ((ntotal,II. + (ntotal,I. + ntotal,II.))/2) ∙ 100 d : distance between the centromere and the d-gene [RU] [RU] : units of recombination ntotal,I. : the total number of ascuses after separation I. ntotal,II. : the total number of ascuses after separation II. Eg,: dcentromere tod- gene = ((88 + (112 + 88))/2) ∙ 100 = 22 RU Háskóli Íslands Raunvísindadeild; Líffræðiskor Erfðafræði Conclusion/Discussion: FIGURE 03, EXAMPLES OF IRREGULAR ASCUSES: 4d:4d 4d:4d 5d:3d 3d:5d 6d:2d 2d:6d A B C A. Segregation has occured after meiosis (PMS)., B. Result from gene conversion., C. Schematic drawing from a microscope. □ Looking at FIGURE 03 ■, one can see some examples of mutated ascuses, called irregular ascuses. Occasionally heteroduplexes are formed according to Hollidays model of recombination. They are DNA-helices hybrids that contain, in this instance, the d+- and d−- gene. When irregular ascuses have 4 dark spores and 4 light spores, 4d+:4d−, then no additional chanegs have occured in the heteroduplexes formed. Therewithal, segregation has occured after meiosis (PMS, post meiotic segregation), as interconverion between the d-genes has taken place. When the ratio of d+ to d− is unequal, ie, 5d+:3d−, 3d+:5d−, 6d+:2d−, or, 2d+:6d−, it is accounted for as gene conversion, taking place after the heteroduplexes has been repaired. Gene conversion is a process which is an exception from the Mendel’s Law. ■ Háskóli Íslands