Meiosis and Genetic Diversity in the Model Organism Sordaria fimicola Lab Report Melissa Luyster Biol 110 Section 034 Introduction The Sordaria lab provides examples displaying the processes of mitosis and meiosis through the life cycles of the microscopic fungus Sordaria fimicola Crossing over a process that occurs during Prophase I of Meiosis I and generates genetic diversity occurs when two homologous chromosomes pair up and exchange genetic material Crossover frequency is the frequency that chromosomes cross over Although crossing over is random little is known about the mechanisms that control crossing over Sordaria has many advantages that make it a good model organism for a crossing over study They have a rapid life cycle are easy to grow in a laboratory are easily viewable under a microscope and make it easy to tell whether or not crossing over took place Research scientists have been using Sordaria fimicola as a model to study the microevolution of mechanisms controlling crossover frequency in response to environmental pressures An evolution canyon is a site used as a research model for their studies named for its potential to see microevolution in several species They are used as research models in the crossover studies The Evolution Canyon I in Israel is narrow valley where the two opposing mountain slopes have differing climatic conditions The south facing slope SFS is exposed to harsh conditions such has high solar radiation which results in high temperatures and drought The north facing slope NFS has more temperate conditions being shadier cooler and more humid Researchers wanted to see if there was a difference in crossover frequencies between strains of Sordaria because of the differences in environment of the opposing slopes Researchers crossed strains from within the same slope north south facing vs north south facing as well as from opposite slopes north facing vs south facing They found the most differences in crossover frequency between opposing slopes The result of their study was that the south facing slope showed a higher crossover frequency compared to the strains from the north facing slope This could potentially be because of the harsh environmental pressures affecting the crossing over mechanisms on the south facing slope Scientists have a strong understanding of when crossing over occurs as well as its consquences However not much is known about what actually controls the process Thus by growing Sordaria in a controlled environment the researcher can look at the mechanisms of crossing over in a more timely manner than watching crossing over in organisms found in evolution canyons If populations are grown under optimal lab conditions baseline information is needed about crossover frequencies of the spore color gene from those populations This is because they must have information to compare to the results under extreme climate conditions The purpose of the experiment performed in Biology 110 was to calculate the baseline frequencies of lab strains to compare to results under extreme conditions Different asci ratios are produced through crossing over The three different types of asci are 4 4 2 2 2 2 and 2 4 2 The 4 4 type occurs when there is no recombination the 2 2 2 2 type occurs when chromosomes line up next to one another and recombine and the 2 4 2 type occurs when the chromosomes are on top of each other and recombine These ratios refer to the colored patterns located on the asci In a 4 4 ratio four black spores and four tan spores are lined up In a 2 2 2 2 ratio the colors alternate every two spores In a 2 4 2 ratio an example would be two black spores four tan spores and two black spores These colors are determined by which type of Sordaria passed on its genes Several research questions are trying to be answered by this experiment What challenges arise in using the provided procedure for mating different strains of Sordaria What challenges arise in preparing squashes of perithecia for scoring asci using the provided procedure What evidence demonstrates that crossing over occurred between the spore color gene and the centromere What is the crossover frequency of the spore color gene with the centromere in organisms grown under optimal growth conditions What is the map distance between the spore color gene and the centromere predicted by the crossover frequency under optimal growth conditions In this experiment crossing over was done between tan and wild type strains of Sordaria Using mating agar plates two different strains were alternated around the plate The dishes were covered and the strains underwent an incubation period of two weeks at room temperature during which they were allowed to reproduce and recombine After two weeks perethecium squashes of the asci were made and scored to find the recombination ratio and the crossover frequencies Each lab partner counted twenty different asci and compared with one another and then compared with the class Methods Crosses were set up using a mating agar plate tan and wild Sordaria strains a scalpel and marking pens Before setting up the mating plates the working station and utensils were sanitized to prevent cross contamination Using the marking pens the mating agar was split into four equal quadrants Two sections diagonal from one another were labeled tan Another two diagonal sections were labeled wild type Next two 0 5 mm squares of agar containing tan Sordaria fungal hyphae were cut from the culture plates and placed into the tan quadrants The same was then done for the wild type Sordaria The lid was securely taped onto the mating plate and labeled with the group number and section and left to incubate at room temperate approximately 70 degrees F for two weeks The perithecium squashes were prepared by adding a small drop of water onto a glass slide Then using an inoculating loop some of the mature recombinant asci was collected from the agar plates and placed onto the slide The slide was covered with a coverslip and examined under a 400x microscope to determine the recombination pattern Each group member counted 20 asci and their patterns 2 4 2 2 2 2 2 4 4 were recorded Three sections individual group and section were used to analyze sort the information There were several calculations used to find the frequency and map distances To determine the total number of asci the calculation used was of 4 4 asci of 2 2 2 2 asci of 2 4 2 asci total number of asci To determine the number of asci produced