Meiosis and Genetic Diversity in Sordaria
Biology 110 Lab
In Israel there exists multiple spots in the mountains called Evolution Canyons, which are all located between a southern facing slope (SFS) and a northern facing slope (NFS). What’s particularly interesting about these locations is that despite the two slopes being on opposite sides of a small canyon, they exhibit extremely contrasting conditions. The SFS receives multiple times the UV radiation from the sun that the NFS receives, has fluctuating weather, and is generally an arid and less hospitable region compared to the temperate, stable environment of the NFS. Scientists collected wild type Sordaria fimicola inhabiting both slopes and discovered that the strains from the SFS exhibited higher mutation rates (more crossover of genes) than those from the NFS. This observation could be attributed to the conditions of the SFS, which are far harsher and more unpredictable than those of the NFS; organisms living in those kind of conditions reasonably should exhibit greater mutation and crossover of genes in order to boost genetic diversity which should allow for organisms to better adapt to changing conditions and still maintain their fitness. This experiment is meant to study this phenomenon under controlled lab conditions to observe how the crossover frequencies of S. fimicola may change under the “environmental stresses” of standard lab conditions. The general hypothesis for this experiment is that if increased crossover and mutation of DNA occurs in organisms when they are subjected to more extreme and variable conditions, then the S. fimicola strains grown in “optimal” and constant laboratory conditions should exhibit less crossover of genes. Without any pressing environmental stresses on the fungi, the tendency for genes to switch positions and need for increased genetic diversity should in fact be diminished. Two different strains of S. fimicola (tan mutant strain, gray wild type strain) will be incubated and allowed to grow in a petri dish for two weeks; after that, mature perithecia will have developed in areas where the two strains’ growth overlapped. The perithecia are to be scraped from the dish and prepared into a squash, which will be examined under a microscope. The final step includes scoring a sample of asci and recording the amounts of each of the three possible patterns before calculating the percentage of crossover in the entire sample.
Materials and Methods:
The experiment was divided into two stages: growing two different mating types of fungi in a single location and allowing them to exchange genes, as well making squashes of the mature perithecia and examining them to determine the degree of recombination that the final asci exhibited following the growth period. The first part begins with retrieving an agar plate and using a marker to draw on the bottom of the plate in order to divide it into four separate quadrants. The four quadrants should each also be marked with a letter for the corresponding mating type that will grow there: two pairs of fungi samples will be used so one should mark two opposing corners of the plate with “T” (tan strain), and other pair of opposing corners with “W” (wild type strain). This set up (pictured below in Figure 1) makes sure strains are alternated so no two adjacent quadrants have the same strain, in which case no recombination could occur.
The marked up plate should then be taken to the lab in order to place the Sordaria samples onto the four sections of agar. Retrieve a scalpel and use a disinfecting wipe to clean the scalpel as well as the work surface; using the cleaned scalpel cut two small squares of the agar containing the hyphae of the tan fungus and place them in their corresponding sections before repeating these step with the wild type fungus. Finally, disinfect the scalpel before returning it and seal the mating plate with tape before allowing it...
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