The purpose of the Sordaria Lab was to explore the affects of genetic variation caused by meiosis and to record how sexual reproduction] affects the amount of crossing over in certain strains of Sordaria Fimicola. These organisms are ascomycetes and are also known as sac fungi. This is because the shape of their asci is in the form of a sac; inside each sac there are structures called ascospores. It is these structures, ascospores, where genetic variation that arises from crossing over is easily seen (Davidson). The organism Sordaria Fimicola is a good example of this process because it is easy to grow on agar plates and because they are easy to be seen when looked at through a microscope (Davidson). There are three strands of Sordaria Fimicola used in this experiment; all were retrieved from an area known as the Evolution Canyon. The Evolution Canyon has two slopes. One is the North Facing Slope that experiences a temperate climate while the South Facing Slope experiences a harsher climate (Sordaria Genetics…). Samples of each type of Sordaria Fimicola were taken from each of the slopes and the third sample, the control group, was a wild type.
When combining each type of Sordaria Fimicola with the wild type, sexual reproduction will occur; the process that allows this to happen is called meiosis. In this lab, the goal is to determine the cross over frequencies of the strains of Sordaria Fimicola. To accomplish this, one must know what meiosis is and how crossing over occurs during meiosis. The overall process of meiosis reduces one diploid cells (2N) into four haploid cells (1N); these haploid cells are referred to as gametes and are the reproductive cells (Meiosis and…). There are four stages of meiosis and the cell undergoes each process twice, prophase, metaphase, anaphase, and telaphase (Meiosis and…). In Meiosis I the cell is reduced from 2N to 1N and there are now two daughter cells. Only during the process of Meiosis I does crossing over (the exchange of identical parts of homologous chromosomes) occur; it occurs in Prophase I (Crossing Over). Then the cell goes through another round of meiosis that produces two more 1N cells for a total of 4 haploid spores. In Sordaria Fimicola the cells then undergo one round of mitosis to create 8 haploid spores. Though it is expected that sexual reproduction does create a great amount of genetic diversity, not all of the asci in Sordaria Fimicola experience crossing over. Figure 1 is a representation of what an asci with no crossing over would look like while Figure 2 shows the different types of recombination possible in these organisms (Mitosis and Meiosis).
Figure 1:Figure 2:
The objective of this lab experiment was to prove that sexual reproduction leads to genetic variation among organisms because of the crossing over that takes place. In this experiment a wild type of Sordaria Fimicola and a tan mutant will be placed on an agar dish and incubated for two weeks. The same process is used for the wild type and the gray mutant. After the two weeks the newly produced Sordaria Fimicola will be analyzed under a microscope and the cross over frequencies will be calculated from the information gathered. It is predicted that when two strains of Sordaria Fimicola are forced to reproduce sexual, then crossing over will occur which will, in turn, increase the amount of genetic variation.
Materials and Methods:
In this experiment, we were recording the cross over frequencies between two different types of mutant Sordaria Fimicola (tan and gray) when they reproduced with a control group (wild type Sordaria Fimicola).
The materials needed for this experiment include:
1. Three strains of Sordaria (wild type, gray, tan),
2. 2 agar dishes
4. Marking pen
7. Cover slip
8. Squirt bottles of water
9. Disinfecting wipes