CROSSING OVER IN Sordaria

1. CROSSING OVER IN Sordaria By Mrs. Jones

2. Common Characteristics of Fungi • eukaryotic • most are multicellular • Reproduce by spores • Sexual or asexual • heterotrophic • absorptive nutrition

3. Structure of a Fungus • hyphae • mycelium (mass of hyphae) • Septa (cross walls) • chitin cell wall • haploid except during sexual reproduction mycelium hyphae septa

4. CLASSIFICATION OF THE FUNGI Eubacteria Chytridiomycota Animals Archae Zygomycota Fungi Eukaryotes Basidiomycota Plants Ascomycota Algae Viruses ? Protists

5. Ecological Impact of Fungi • decompose wastes and dead organisms • return nutrients to the ecosystem • Saprophytic fungi = absorb nutrients from decaying material • decomposers • in one year over a tone of debris falls onto an acre of woodland floor

6. Pathogenic Fungi Valley Fever • Coccidioidesimmitis, • grows in soils in areas of low rainfall, high summer temperatures, and moderate winter temperatures. • spores become airborne when disturbed by winds, construction, farming and other activities. • infection occurs when a spore is inhaled • symptoms generally occur within three weeks of exposure • is not "contagious" , meaning it is not passed from person to person athletes foot fungal infection lives on skin a breeds under warm, moist conditions more common during hot weather sweaty footwear is usually the culprit

7. Pathogenic Fungi Cont. • Powdery mildews that attack ornamental and food plants • The 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.

8. Food Source • The 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 yeast • Ferments sugar to ethanol and carbon dioxide and thus is used to make alcoholic beverages like beer and wine • to make ethanol for industrial use • in 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 Tuber morel

9. Sordaria Life Cycle

10. Life Cycle of Sordaria • The ascospore is haploid. • It divides by mitosis producing haploid filaments • As it continues to divide by mitosis the haploid mycelium grow inside the organism the fungus is digesting

11. Life 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.

12. Life Cycle Cont. • The 8 nuclei develop into ascospores. • The spores are discharged from the perithecium and the cycle begins again.

13. Wild and tan strains being crossed on agar plate. Where the mycelia of the two strains meet fruiting bodies called perithecia develop.

14. Perithecium containing asci.

15. When the perithecia are crushed the asci can be seen.

16. Sordaria ascus (non hybrid) Fertilization did not take place between different strains of fungi. If genes crossed over we cannot tell because all of the spores are the same color.

17. Asci containing black and tan ascospores.

18. Formation of asci During 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.

19. Chiasmata (crossing over)

20. A Closer Look at Chiasmata The + designate wild type genes (black) tn designates the mutant with tan spores. When no crossing over occurs the tan asci will all be together and the black asci will all be together.

21. Asci showing no crossing over.

22. Meiosis with Crossing Over When crossing over occurs the ascospores will form one of the patterns above . Notice that only half of the chromosomes crossed over . This means that half of the spores in the ascus are the result of crossover.

23. Ascospore showing crossover.

24. Materials • perithecia (paper bag) from a black X tan cross • asci (paper strips) with eight dots representing ascospores

25. Procedure • remove the ascifrom the bag and separate into hybrid and nonhybrid stacks. • separate and count the MI and MII asci • do NOT count the nonhybridasci • record your personal data in your lab book and in the class data in the computer.

26. Calculate 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-over • divide the percent of cross-over by 2 to calculate the map distance

27. Questions • 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.

28. GLOSSARY Absorptive nutrition - obtaining nourishment from the surroundings (often having first digested it by secreting enzymes) Dikaryotic – possess two haploid nuclei Diploid – the presence of pairs of homologous chromosomes Haploid – single chromosomes NOT pairs Heterotrophic –obtaining nutrients by eating other organisms or their byproducts. Pathogenic – disease causing