2MAIN MENU Intro to the fungi Sordaria Life Cycle Structures of SordariaFormation of AsciLab
3Common Characteristics of Fungi eukaryoticmost are multicellularReproduce by sporesSexual or asexualheterotrophicabsorptive nutrition
4Structure of a Fungus hyphae mycelium (mass of hyphae) Septa (cross walls)chitin cell wallhaploid except during sexual reproductionmyceliumhyphaesepta
5CLASSIFICATION OF THE FUNGI EubacteriaChytridiomycotaAnimalsArchaeZygomycotaFungiEukaryotesBasidiomycotaPlantsAscomycotaAlgaeViruses ?Protists
6Ecological Impact of Fungi decompose wastes and dead organismsreturn nutrients to the ecosystemSaprophyticdecomposers in a woodlandOne year over a ton of debris falls onto an acre of woodlandreturn nutrients to the soil.
7Pathogenic Fungi valley fever Valley Fever disease of the common in the southwestern United States and northwestern Mexico. caused by the fungus Coccidioides immitis,which grows in soilsfungal spores become airborne when the soil is disturbedinfection occurs when a spore is inhaledWithin the lung, the spore changes into a larger, multicellular structure called a spherule. The spherule grows and bursts, releasing endospores which develop into spherules..
8a fungal infection. athletes foot lives on the skin and breeds under warm, moist conditions.more common during hot weathersweaty footwear is usually the culprit. Adult males suffer most often from this condition.
9Pathogenic Fungi Cont.Powdery mildews that attack ornamental and food plantsThe chestnut blight, which in a few decades killed almost all of the mature American chestnut trees in the Appalachians of North America.The Dutch elm disease, which has killed many of the American elms in the United States.
10Food SourceThe truffle and the morel are both highly-prized food delicacies. Truffles establish a symbiotic relationship with the roots of such trees as oaks.Saccharomyces cerevisiae or budding yeastFerments sugar to ethanol and carbon dioxide and thus is used to make alcoholic beverages like beer and wineto make ethanol for industrial usein baking (it is often called baker's yeast). Here, it is the carbon dioxide that is wanted (to make bread and cakes "rise" and have a spongy texture).Oregon White Truffle Tubermorel
12Life Cycle of Sordaria The ascospore is haploid. It divides by mitosis producing haploid filamentsAs it continues to divide by mitosis the haploid mycelium grow inside the organism the fungus is digesting
13Life Cycle Cont. The ends of two mycelia fuse. The nuclei of two haploid cells join (fertilization) forming a diploid zygote.The zygote then divide by meiosis producing 4 haploid cells.The four cells divide by mitosis producing 8 haploid nuclei.
14Life Cycle Cont. The 8 nuclei develop into ascospores. The spores are discharged from the perithecium and the cycle begins again.
15Wild and tan strains being crossed on agar plate Wild and tan strains being crossed on agar plate. Where the mycelia of the two strains meet fruiting bodies called perithecia develop.
20Formation of asciDuring prophase I of meiosis homologous chromosomes pair and form tetrads through the process of synapsis. While the four chromosomes are close together DNA can be exchanged between homologous chromatids.
22A Closer Look at Chiasmata The + designate wild type genes (black)tn designates the mutant with tan spores.When no crossing over occurs the tan asciwill all be together and the black asci will all be together.
24Meiosis with Crossing Over When crossing over occurs the ascospores will formone of the patterns above .Notice that only half of the chromosomes crossed over .This means that half of the spores in the ascus are theresult of crossover.
26Mapping the Genes of Sordaria OBJECTIVESExplain how meiosis and crossing-over result in different arrangements of ascospores within the asciCalculate the map distance between a gene for ascospore color and the centromere of the chromosome on which the gene is found.
27BackgroundThe frequency of crossing over appears to be governed largely by the distance between genes, or in this case, between the gene for spore coat color and the centromere. The probability of a crossover occurring between two particular genes on the same chromosome (linked genes) increases as the distance between those genes becomes larger. The frequency of crossover, therefore, appears to be directly proportional to the distance between genes.
28A map unit is an arbitrary unit of measure used to describe relative distances between linked genes. The number of map units between two genes or between a gene and and the centromere is equal to the percentage of the recombinants. Customary units cannot be used because we cannot directly visualize genes with the light microscope. However, due to the relationship between distance and crossover frequency, we may use the map unit.
29Materials perithecia (paper bag) from a black X tan cross asci (paper strips) with eight dots representing ascospores
30Procedureremove the asci form the bag and separate into hybrid and nonhybrid stacks.separate and count the MI and MII ascido NOT count the nonhybrid ascirecord your personal data in your lab book and in the class data in the computer.
31Calculate Map Distance (use the class data) divide the number of cross-over asci by the total number of asci and multiply by 100 to calculate the percent of cross-overdivide the percent of cross-over by 2 to calculate the map distance
32Questions Why are the nonhybrid asci not counted? Why is the percent of cross-over divided by 2?Draw a pair of chromosomes in MI and in MII, and show how you would get a 2:4:2 arrangement of ascospores by crossing over.
33GLOSSARYAbsorptive nutrition - obtaining nourishment from the surroundings (often having first digested it by secreting enzymes)Dikaryotic – possess two haploid nucleiDiploid – the presence of pairs of homologous chromosomesHaploid – single chromosomes NOT pairsHeterotrophic –obtaining nutrients by eating other organisms or their byproducts.Pathogenic – disease causing