Effects of Crossing Over in Sordaria fimicola
Sexual reproduction in organisms is a cause for genetic variation. This can be seen through the process of meiosis in Sordaria fimicola because of the effects of crossing over and independent assortment that occur in meiosis I. Before performing this experiment we hypothesized that we would be able to see that crossing over did indeed occur in the S. fimicola. We tested our hypothesis by growing our own culture and observing it under a microscope. By counting and recording the types of asci we were able to find that our hypothesis had been correct. This has now led us to know that sexual reproduction causes an increase in genetic variation in organisms such as, Sordaria fimicola.
Organisms reproduce in two ways: asexually and sexually. Sexual reproduction can be defined as the reproduction involving the union of gametes or when genetic material from two parents combine to form offspring (Cyr). Offspring produced from sexual reproduction have a unique genetic make-up, which can either be beneficial or destructive to them (Saleem). Close to all known organisms use this kind of reproduction during some moment in their lifetime. If this is true, however, why is not every species seemingly genetically identical? To answer this, one must observe the chromosome behavior during the sexual reproduction life cycle also known as meiosis.
Meiosis is the process of cell division in which gametes are produced. It results in four haploid (IN) cells from two diploid (2N) cells (Cyr). In meiosis I, crossing over and independent assortment of the chromosomes occur. These two processes increase the genetic variation within the cell either benefiting or hurting the cell’s ability to adapt (natural selection). After these two events have occurred, the chromosomes will then proceed through all four stages and produce two daughter cells (Cyr). In meiosis II, the two daughter cells each again proceed through all four stages and produce a final four distinctly different daughter cells (Cyr). Sordaria fimicola allows us to see observe the process of meiosis. This is because its life cycle is rapid and allows scientists to observe many generations in a short amount of time (Meiosis). Also, the size of S. fimicola makes it easily viewable under a microscope.
Experiments with “Evolution Canyon” have shown exactly how S. fimicola is a representative organism for crossing over. Evolution Canyon represents the whole idea of different locations in Israel containing two mountain slopes exposed to vastly different climatic conditions that converge with a valley between them (Meiosis). In each of these cases, one slope has been exposed to harsh conditions while the other has been exposed to temperate conditions (Saleem). Because each slope undergoes different conditions, we can observe how genetic variation is affects the S. fimicola that live on each slope. Scientists gathered samples of the organism living on both slopes and analyzed the differences in crossing over and the differences in crossing over frequencies.
The purpose of our lab is to observe the different cross over frequencies. We want to compare and contrast the crossover frequencies in different color strains of S. fimicola. We hypothesize that in this experiment we will observe crossing over occur in the Sordaria fimicola after two weeks of growth in the agar plates. To test our hypothesis, we will grow our own asci spores in an agar plate and observe the organism under the microscope while recording the different ascus types which can either be type A (4:4), type B (2:4:2), or type c (2:2:2:2).
Materials and Methods
From the ‘Meiosis and Genetic Diversity in Sordaria’ handout, we found the materials and procedure for this experiment. Equipment that we needed to perform the first part of this experiment were two agar plates, a marking pen, a scalpel, and two different color strands of S....
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