Meiosis and Genetic Diversity in Sordaria

Introduction

Sordaria fimicola is an ascomycete fungus studied for its product of meiosis and mitosis that form 8 haploid spores. These spores are contained in a fruiting body called perithecia. Asci made up of spores are contained in this body. The perithecia are squashed in order to better identify the asci. Scuderia is a very beneficial organism to study genetic variation because it is maintainable in a lab, has a short life cycle, its asci are easily distinguishable under a microscope and it helps to understand meiosis. Sordaira is found in Evolution canyon. It is a place in Israel that is a natural setting to explore the relations of organisms and their environment. Each side of the canyon is very different. One side is exposed to harsh conditions and much sun exposure while the other has more moderate conditions. The European slope of the canyon has a dark gray landscape while the African slope has a lighter brown landscape. Meiosis is a reduction process that reduces diploid cells to haploid cells(2N1N). Meiosis I cause genetic variation to occur through the process of crossing over and independent assortment.

Two haploid daughter cells are formed at the end of Meiosis I. Meiosis II then forms four haploid daughter cells. Every cell differs in its genetic material. Mitosis then creates 8 spores. These spores can have combinations of tan or gray to wild such as 4:4, 2:4:2, and 2:2:2:2. When the spores mature, they will be released. Two haploid cells will then unite through fertilization to form a diploid zygote. This lab will further our knowledge of meiosis and the benefits of genetic variation in Scordaria fimicola. Two types of fungi were used to show the effects of crossing over and independent assortment.

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The fungi combinations were created by placing two samples of tan or gray type on an agar plate and two samples of wild type and allowing them to combine over two weeks. After this amount of time, the perithecia are well enough developed and are able to be squashed. The spores show different color combinations due to the meeting of wild and mutant type fungi. The mutant types will show light tan or gray color and the wild shows a dark spore. This will show us the combinations of spores created from meiosis and mitosis. It is expected that all three combinations of asci will be shown. It is expected that the tan type will show more recombinant asci than the gray type. The purpose of this experiment is to show the distance between gene and centromere as well as the importance of sexual reproduction and genetic variation.

Methods

Two agar plates were set up to allow the spore mutations to occur. Each plate was divided into four sections. Wild and tan or gray type Sordaria was placed in opposing sections of the plate. The plates were then left to incubate for two weeks. After the two weeks, samples were taken from the plate and then squashed onto a microscope slide in order to burst the perithecia to view the asci. Crossover frequencies were measures by counting the frequency patterns of asci within an ascus cluster. Map distances, which measures the distance from gene to centromere, were then calculated after asci totals were found. The results mean that there was 29. 7 mu for tan and 28. mu for gray between the crossing over and the centromere. Taking results from such a large group of data makes for a more accurate result. The image shows the possible combination of outcomes of sordaria. The first one shows no crossing over (4:4) and the next two show crossing over with results (2:2:2:2 and 2:4:2).

Discussion

This experiment helped us to better understand the importance of crossing over in sexual reproduction and also meiosis. The results showed that the Sordaria were more likely to cross over. With 59. 4% and 57. % recombinant, a majority of Sordaria show genetic independence. Genetic independence allows for Sordaria to survive, adapt, and continue reproducing. They produced different offspring due to meiosis and mitosis. The two percent difference could be possible due to the different spore strains and their optimal conditions. Within the experiment, several errors could have occurred. One of the implications could have been the counting of the asci. When viewing them from a microscope it is very difficult to keep track of every single ascus. Some could have been double-counted or missed entirely. Another possible experiment would be to test a larger sample. Larger samples allow for more accurate results. A second experiment would be to test another organism that experiences the process of meiosis and mitosis through asexual reproduction. A third experiment could carry out the same process but under different conditions to see if the results show the same pattern. In conclusion, Sordaria fimicola showed the process of crossing over and meiosis. It displayed the importance of genetic variation for use of survival and adaption.

Reference

1. “Bio 110 Lab Activity: Meiosis and Genetic Diversity in Sordaria, week of September 24th. ” Pennsylvania State University in 2011.
2. Volk, Thomas. "Sordaria Fimicola, a Fungus Used in Genetics-- Tom Volk's Fungus of the Month for March 2007".
3. Sordaria fimicola, a Fungus Used in Genetics-- Tom Volk's Fungus of the Month for March 2007. University of Wisconsin, 2007. Web. 25 Oct. 2012.
4. http://botit. botany.wisc.edu/toms_fungi/mar2007. html>.

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