Neurospora LIFE CYCLE
An ascocarp, or ascoma (plural: ascomata), is the fruiting body (sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and may contain millions of asci, each of which typically contains four to eight ascospores. This is similar to a perithecium, but the asci are not regularly organised into a. It is the dark brown perithecium on the agar plate that you can observe with the By observing the order of the ascospores in the ascus one can determine the. There it is explained that members of the Sordariomycetes have perithecia that begin as The other defining feature of the Dothideomycetes is the bitunicate ascus. The very dark objects inside the ascus are the four-celled ascospores.
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Unsourced material may be challenged and removed. June Asci of Morchella elataPhase contrast image There are 8 ascospores in each ascus of Sordaria fimicola. Asci usually contain eight ascosporesproduced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or species can occur in numbers of one e.
Monosporascus cannonballustwo, four, or multiples of four. In a few cases, the ascospores can bud off conidia that may fill the asci e. Tympanis with hundreds of conidia, or the ascospores may fragment, e. Ascospores are nonmotile, usually single celled, but not infrequently may be coenocytic lacking a septumand in some cases coenocytic in multiple planes.
Mitotic divisions within the developing spores populate each resulting cell in septate ascospores with nuclei. The term ocular chamber, or oculus, refers to the epiplasm the portion of cytoplasm not used in ascospore formation that is surrounded by the "bourrelet" the thickened tissue near the top of the ascus. In other cases, such as single-celled yeastsno such structures are found. In rare cases asci of some genera can regularly develop inside older discharged asci one after another, e.
Heterothallic as above means that there are two mating types that must unite to be able to go through the sexual cycle which includes meiosis. The two mating types look identical. These two mating type sequences are totally different, so they do not represent alleles; instead they are called idiomorphs. Click picture for larger image Diagram of fertilization and perithecium courtesy of T. A squashed perithecium of N.
Raju A diagram of ascus development courtesy of N. Raju If the two mating types are inoculated on a petri dish, a single or double line of fruiting bodies perithecia from between them.
DISCUSSION OF THE DOTHIDEOMYCETES
Image courtesy of M. Smith Homothallic means that any haploid individual strain can go through the sexual cycle by itself, without pairing with another strain. Homothallic species do not need both MAT idiomorph sequences, but in some cases one or the other can be detected in the genomic sequence.
This process is called tetrad analysis since the outcome of meiosis in Ascomycetes results in a linear tetrad of haploid spores. By analyzing spore patterns one can observe crossover events that occurred during meiosis when an allelic marker is located on each chromatid of a synapsed tetrad.
Ascocarp - Wikipedia
Such an analysis reveals two important pieces of information about the crossover event. First, one can determine which two of the four chromatids participated in the cross over event. Secondly, the gene can be mapped relative to an observable cytological marker such as the centromere. By determining the location of several genes, one could eventually determine linkage groups and chromosome locations for all genes.
Sordaria fimicola is a common species of ascomycete found on dung. Sordaria is haploid and spends most of its life cycle in the vegetative state. This occurs by the creation of the a binucleate hypha, and the eventual fusion of the two nuclei within a developing ascus fuse to produce a diploid 2n zygote.
In the case of Sordaria the meiotic division is followed by a mitotic division to produce eight ascospores Figure 1.
SEXUAL REPRODUCTION BY MEANS OF ASCI
The asci about 20 are grouped together within a structure called the perithecium. It is the dark brown perithecium on the agar plate that you can observe with the naked eye.What does apothecium mean
When you observe the Sordaria in this lab, you will note that the ascospores are of two different colors. The mutant form of this gene called "tan" t produces a light spore.
Ascomycota, Ascomycetes & Sac Fungi
By observing the order of the ascospores in the ascus one can determine the order in which the chromosomes are segregated separated during meiosis. If no crossover events occur, the two genes will segregate during meiosis I and produced a 4: In the following exercise you will begin by make a cross between Sordaria with the wild type ascospore color dark and Sordaria with the mutant ascospore color tan. Then, after about 11 days of culture, you will observe the color sequence of ascospores produced in the hybrid asci.
From your observations you will be able to calculate the gene to centromere distance in map units.
Keep in mind that the centromere is telomeric. Each student should obtain a starch agar petri plate from the instructor. This plate will be designated the cross plate, and will be used to cross the wild type dark ascospore Sordaria with the mutant type tan ascospore Sordaria. On the bottom of the cross plate write your initials. With the cross plate upside down, center the petri plate over Figure 3 below.
Now turn the plate right side up. There are two stock plates of Sordaria that will be circulating round the lab room. When the plates come to you, slightly lift the cover of the stock petri plate and, using a sterile toothpick, transfer a block of the fungi culture to your starch plate.