Sordaria Research Paper
“Meiosis and Genetic Diversity in the Model Organism, Sordaria fimicola”
November 4, 2013
Biology 110- Basic Concepts and Biodiversity Fall 2013
I. Introduction
The Earth is home to various forms of life contributing to the endless biodiversity that we see in our daily lives. In environments around the world there are distinct correlations between the environment and adaptations acquired by the organisms that live there. It has been shown that these adaptations are a result of crossing-over events that occur during meiosis. This exchange of DNA sequences give rise to organisms that will survive successfully in certain environments (Cyr, R. 2002). This is seen clearly on the Slopes of Evolution Canyon …show more content…
(Singaravelan et.al 2010). This canyon in Israel contains two slopes, one of harsh climate (South Facing) and one of temperate climate (North Facing), each with organisms living independently and successfully (Cyr, R. 2002). There have been many studies done there such as the spiny mouse modulate (Singaravelan et.al 2010). This study proved that an adaptation such as pigment could be a result of mating among organisms influenced by the environment. That is just one example of how the environment molds organisms to survive successfully, which in turn make organisms better, adapted to their environment allowing them to survive successfully and produce more offspring.
To provide a closer look at how genetic variation comes about, researchers have used the model organism, Sordaria Fimicola to study the frequency of crossover events in relation to environmental pressures.
Sordaria is an Ascomycota that uses a special spore formation process in reproduction. Ascomycota’s use both meiosis and mitosis division to produce eight spores (asci). These asci are held in a sac called a perithecium or ascus, a fruiting body that rupture and release the ascospores when they’ve reached maturity (Cyr, R. 2002). These spores are easily viewed under a microscope and have mutant strain colors with different patterns that serve as proof of crossover events. Wild-type (black spores) and non-black spores (tan) we used to detect crossing over. The asci can be arranged in 4:4: meaning 4 black spores and 4 tan spores, which indicate no crossing over occurred. Asci can also be arranged with alternating tan and black in groups of two. 2:4:2 arrangements also occur meaning 2 black spores, 4 tan then another 2 black spores. 2:2:2:2 and 2:4:2 are both an indication that crossover has taken place. When spores of the organism were crossed with strains from the same slope and from different slopes, it was found that the crossover frequencies were greater on the South Facing slope rather than on the North Facing Slope (Hass, C. and Ward, A. 2010). These findings led to a correlation between harsher environments and high cross over frequencies and also many questions.
In this experiment, we mimicked the first round experiments of setting up crosses between wild type and spore color strains to examine the changes in cross over frequency of Sordaria under normal, baseline
conditions.
Four small pieces of agar of different strains (tan or black) were placed on a plate alternated in 4 squares marked on the plate. The plates were covered, taped, and left to incubate for 2 weeks. Once the incubation period was over, squashes of asci were prepared. The squashes were observed under a microscope and cross over events were tallied in order to ultimately calculate the crossover frequencies. Through these procedures, 5 research questions were to be answered. 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 in 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? (Hass, C. and Ward, A. 2010)
II. Materials and Methods (Hass, C. and Ward, A. 2010. )The crosses were set up by first dividing the plate into fourths and placing 2 small pieces of wild type (black) Sordaria and tan Sordaria strains alternating on the plate as shown in the diagram on the previous page. These plates were then covered and sealed shut with tape and placed in an incubator at room temperature for two weeks to insure proper reproduction. After the incubation period, squashes were prepared. A sample of Sordaria was taken from the area of most recombination (on the dividing lines of the plate) using a toothpick and was placed on a slide with a drop of water and a coverslip on top. The eraser of a pencil was used to press down on the cover slip to break the spores apart in order to see the pattern of wild and tan type spores under the microscope. Once squashed and under the microscope, 20 patterns were found and tallied in order to calculate the crossover frequency. To find the recombination percentage the number of asci of the 2:2:2:2 and 2:4:2 patterns were added and then dived by the total number of asci and multiplied by 100. Map distance (the distance between genes starting from the centromere of the chromosome) was calculated by dividing the recombination percentage by two. This is unique to Sordaria because only half of the spores go through the crossing over process.
Sordaria Mating Plate Before Incubation
Wild Type
Tan
Sordaria Mating plate after two weeks of Incubation
Where samples were taken from
Different Arrangements of Sordaria through Cross Over Events
Step 1: Crossing Over
Step 2: Meiosis I
Step 3: Meiosis II
Step 4: Mitosis
*No crossing over occurred * Crossing over occurred
III. Results
Table 5. Combined Section Data Analysis of Sordaria spore patterns under a microscope
Non-Recombinant
Recombinant
Total # of Asci
Total # Recombinant Asci (B+C)
Frequency of Recombinant Asci (B+C/total # asci)
Frequency of Type B Asci (B/total # asci)
Frequency of Type C Asci (C/total # asci)
Ratio B/C
# of Type A Asci (4:4)
# of Type B Asci (2:4:2)
# of Type C Asci (2:2:2:2)
240
144
60%
37.1%
22.9%
1.6
96
89
55
Map Distance: Frequency of Recombinant Asci (B+C/total # of asci)/2
60%/2 = 30 map units (mu)
IV. Results Continued
Non-Recombinant
Recombinant
Total # of Asci
Total # Recombinant Asci (B+C)
Frequency of Recombinant Asci (B+C/total # asci)
Frequency of Type B Asci (B/total # asci)
Frequency of Type C Asci (C/total # asci)
Ratio B/C
# of Type A Asci (4:4)
# of Type B Asci (2:4:2)
# of Type C Asci (2:2:2:2)
16,371
10,013
61.2%
31.2%
29.9%
1.04
6358
5105
4908
Table 6. Combined Course Data Analysis of Sordaria spore patterns under a microscope
Map Distance: Percent of crossing over/2
61.2%/2 = 30.6 mu
V. Discussion
This experiment showed the processes of Mitosis and Meiosis and their contribution to genetic variation through cross over events. Observations of the different arrangements of tan and wild type spores on the asci pods gave a clear outlook on reproduction processes through use of microscope. The data provides evidence to support this crossover phenomenon and provides answers to the research questions introduced at the start of this laboratory exercise.
When the patterns of the asci were scored and used to calculate the total frequency and recombination, crossover events( 2:4:2 and 2:2:2:2 patterns of spores) occurred around 60 percent of the time in both the combined section data and the combined course data. This frequency is an indication that 60 percent of the Sordaria population is genetically independent. This significant amount of crossing over considering the standard conditions of the experiment is critical for the organism to survive successfully in its environment. Consequently, the map distance between the spore color gene and the centromere of the chromosome was approximately 30 percent for both sets of data.
Although these results do provide answers to previous questions and furthers the understanding of genetic variation in organisms, due to the lower quality instruments and inexperienced students, there is a fair amount of chance of error in this experiment. In the beginning stages of the procedure, there is a chance of contamination by airborne particles incomplete sterilization of the tools, which may of led to faulty results. Moreover, there were issues locating specific patterns of asci under the microscope because of the obscurity of the images presented. As a result, spore patterns may have been counted more than once or data from spores printed on a notecard were used which may not be an accurate depiction of crossover events that actually occurred. Simple mistakes such as incorrectly documenting the number of recombinant asci or calculating the total frequency may have also occurred.
With errors aside, this experiment certainly does not dispute the claims of crossing over occurring in the spores of Sordaria and these events leading to genetic variation within the species. This experiment also proves that recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. Now that it is clear that crossing over occurs, to further this experiment and gain more detailed results, testing a larger amount of fungi along with varying the conditions of the plates to emulate the south and north facing climates of the evolutionary canyon may lead to more insight on how the environment directly relates to cross over frequency and leads to genetic independence among a population.
VI. References
1. Cyr, R. 2002. Overview, Life and Natural Selction. In, Biology 110: Basic concepts and biodiverity course website. Department of Biology, The Pennsylvania State University. http://www.bio.psu.edu/
2. Cyr, R. 2002. Fungi II- Phyla Ascomycota and Basidiomycota. In, Biology 110: Basic concepts and biodiversity course website. Department of Biology, The Pennsylvania State University. http://www.bio.psu.edu/
3. Meiosis and Genetic Diversity in the Model Organism, Sordaria. Written by Hass, C. and Ward, A. 2010. Department of Biology, The Pennsylvania State University, University Park, PA.
4. Singaravelan, Natarajan, Tomas Pavlicek, Alex Beharav, Kazumasa Wakamatsu, Shosuke Ito, Eviatar Nevo, and Eric Warrant. "Spiny Mice Modulate Eumelanin To Pheomelanin Ratio To Achieve Cryptic Coloration In “Evolution Canyon,” Israel." PLoS ONE 5.1 (2010): e8708. Print.
November 4, 2013
Biology 110- Basic Concepts and Biodiversity Fall 2013
I. Introduction
The Earth is home to various forms of life contributing to the endless biodiversity that we see in our daily lives. In environments around the world there are distinct correlations between the environment and adaptations acquired by the organisms that live there. It has been shown that these adaptations are a result of crossing-over events that occur during meiosis. This exchange of DNA sequences give rise to organisms that will survive successfully in certain environments (Cyr, R. 2002). This is seen clearly on the Slopes of Evolution Canyon …show more content…
(Singaravelan et.al 2010). This canyon in Israel contains two slopes, one of harsh climate (South Facing) and one of temperate climate (North Facing), each with organisms living independently and successfully (Cyr, R. 2002). There have been many studies done there such as the spiny mouse modulate (Singaravelan et.al 2010). This study proved that an adaptation such as pigment could be a result of mating among organisms influenced by the environment. That is just one example of how the environment molds organisms to survive successfully, which in turn make organisms better, adapted to their environment allowing them to survive successfully and produce more offspring.
To provide a closer look at how genetic variation comes about, researchers have used the model organism, Sordaria Fimicola to study the frequency of crossover events in relation to environmental pressures.
Sordaria is an Ascomycota that uses a special spore formation process in reproduction. Ascomycota’s use both meiosis and mitosis division to produce eight spores (asci). These asci are held in a sac called a perithecium or ascus, a fruiting body that rupture and release the ascospores when they’ve reached maturity (Cyr, R. 2002). These spores are easily viewed under a microscope and have mutant strain colors with different patterns that serve as proof of crossover events. Wild-type (black spores) and non-black spores (tan) we used to detect crossing over. The asci can be arranged in 4:4: meaning 4 black spores and 4 tan spores, which indicate no crossing over occurred. Asci can also be arranged with alternating tan and black in groups of two. 2:4:2 arrangements also occur meaning 2 black spores, 4 tan then another 2 black spores. 2:2:2:2 and 2:4:2 are both an indication that crossover has taken place. When spores of the organism were crossed with strains from the same slope and from different slopes, it was found that the crossover frequencies were greater on the South Facing slope rather than on the North Facing Slope (Hass, C. and Ward, A. 2010). These findings led to a correlation between harsher environments and high cross over frequencies and also many questions.
In this experiment, we mimicked the first round experiments of setting up crosses between wild type and spore color strains to examine the changes in cross over frequency of Sordaria under normal, baseline
conditions.
Four small pieces of agar of different strains (tan or black) were placed on a plate alternated in 4 squares marked on the plate. The plates were covered, taped, and left to incubate for 2 weeks. Once the incubation period was over, squashes of asci were prepared. The squashes were observed under a microscope and cross over events were tallied in order to ultimately calculate the crossover frequencies. Through these procedures, 5 research questions were to be answered. 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 in 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? (Hass, C. and Ward, A. 2010)
II. Materials and Methods (Hass, C. and Ward, A. 2010. )The crosses were set up by first dividing the plate into fourths and placing 2 small pieces of wild type (black) Sordaria and tan Sordaria strains alternating on the plate as shown in the diagram on the previous page. These plates were then covered and sealed shut with tape and placed in an incubator at room temperature for two weeks to insure proper reproduction. After the incubation period, squashes were prepared. A sample of Sordaria was taken from the area of most recombination (on the dividing lines of the plate) using a toothpick and was placed on a slide with a drop of water and a coverslip on top. The eraser of a pencil was used to press down on the cover slip to break the spores apart in order to see the pattern of wild and tan type spores under the microscope. Once squashed and under the microscope, 20 patterns were found and tallied in order to calculate the crossover frequency. To find the recombination percentage the number of asci of the 2:2:2:2 and 2:4:2 patterns were added and then dived by the total number of asci and multiplied by 100. Map distance (the distance between genes starting from the centromere of the chromosome) was calculated by dividing the recombination percentage by two. This is unique to Sordaria because only half of the spores go through the crossing over process.
Sordaria Mating Plate Before Incubation
Wild Type
Tan
Sordaria Mating plate after two weeks of Incubation
Where samples were taken from
Different Arrangements of Sordaria through Cross Over Events
Step 1: Crossing Over
Step 2: Meiosis I
Step 3: Meiosis II
Step 4: Mitosis
*No crossing over occurred * Crossing over occurred
III. Results
Table 5. Combined Section Data Analysis of Sordaria spore patterns under a microscope
Non-Recombinant
Recombinant
Total # of Asci
Total # Recombinant Asci (B+C)
Frequency of Recombinant Asci (B+C/total # asci)
Frequency of Type B Asci (B/total # asci)
Frequency of Type C Asci (C/total # asci)
Ratio B/C
# of Type A Asci (4:4)
# of Type B Asci (2:4:2)
# of Type C Asci (2:2:2:2)
240
144
60%
37.1%
22.9%
1.6
96
89
55
Map Distance: Frequency of Recombinant Asci (B+C/total # of asci)/2
60%/2 = 30 map units (mu)
IV. Results Continued
Non-Recombinant
Recombinant
Total # of Asci
Total # Recombinant Asci (B+C)
Frequency of Recombinant Asci (B+C/total # asci)
Frequency of Type B Asci (B/total # asci)
Frequency of Type C Asci (C/total # asci)
Ratio B/C
# of Type A Asci (4:4)
# of Type B Asci (2:4:2)
# of Type C Asci (2:2:2:2)
16,371
10,013
61.2%
31.2%
29.9%
1.04
6358
5105
4908
Table 6. Combined Course Data Analysis of Sordaria spore patterns under a microscope
Map Distance: Percent of crossing over/2
61.2%/2 = 30.6 mu
V. Discussion
This experiment showed the processes of Mitosis and Meiosis and their contribution to genetic variation through cross over events. Observations of the different arrangements of tan and wild type spores on the asci pods gave a clear outlook on reproduction processes through use of microscope. The data provides evidence to support this crossover phenomenon and provides answers to the research questions introduced at the start of this laboratory exercise.
When the patterns of the asci were scored and used to calculate the total frequency and recombination, crossover events( 2:4:2 and 2:2:2:2 patterns of spores) occurred around 60 percent of the time in both the combined section data and the combined course data. This frequency is an indication that 60 percent of the Sordaria population is genetically independent. This significant amount of crossing over considering the standard conditions of the experiment is critical for the organism to survive successfully in its environment. Consequently, the map distance between the spore color gene and the centromere of the chromosome was approximately 30 percent for both sets of data.
Although these results do provide answers to previous questions and furthers the understanding of genetic variation in organisms, due to the lower quality instruments and inexperienced students, there is a fair amount of chance of error in this experiment. In the beginning stages of the procedure, there is a chance of contamination by airborne particles incomplete sterilization of the tools, which may of led to faulty results. Moreover, there were issues locating specific patterns of asci under the microscope because of the obscurity of the images presented. As a result, spore patterns may have been counted more than once or data from spores printed on a notecard were used which may not be an accurate depiction of crossover events that actually occurred. Simple mistakes such as incorrectly documenting the number of recombinant asci or calculating the total frequency may have also occurred.
With errors aside, this experiment certainly does not dispute the claims of crossing over occurring in the spores of Sordaria and these events leading to genetic variation within the species. This experiment also proves that recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. Now that it is clear that crossing over occurs, to further this experiment and gain more detailed results, testing a larger amount of fungi along with varying the conditions of the plates to emulate the south and north facing climates of the evolutionary canyon may lead to more insight on how the environment directly relates to cross over frequency and leads to genetic independence among a population.
VI. References
1. Cyr, R. 2002. Overview, Life and Natural Selction. In, Biology 110: Basic concepts and biodiverity course website. Department of Biology, The Pennsylvania State University. http://www.bio.psu.edu/
2. Cyr, R. 2002. Fungi II- Phyla Ascomycota and Basidiomycota. In, Biology 110: Basic concepts and biodiversity course website. Department of Biology, The Pennsylvania State University. http://www.bio.psu.edu/
3. Meiosis and Genetic Diversity in the Model Organism, Sordaria. Written by Hass, C. and Ward, A. 2010. Department of Biology, The Pennsylvania State University, University Park, PA.
4. Singaravelan, Natarajan, Tomas Pavlicek, Alex Beharav, Kazumasa Wakamatsu, Shosuke Ito, Eviatar Nevo, and Eric Warrant. "Spiny Mice Modulate Eumelanin To Pheomelanin Ratio To Achieve Cryptic Coloration In “Evolution Canyon,” Israel." PLoS ONE 5.1 (2010): e8708. Print.