During prophase 1 of meiosis, homologous chromosomes line up with each other before they are split apart, one chromosome coming from the father and the other coming from the mother. Before they are split, there is a phenomenon called recombination that occurs, where certain genes from nonsister chromatids will switch with the same genes from its partner.
This means that the chromosome given from the mother will also contain genes from the father, creating a genotype and phenotype that is a combination of the two, and not simply a direct copy of one parent.
Once recombination occurs and meiosis completes itself, the four daughter cells go through mitosis that replicates the formed chromosome and create eight colored spores that demonstrate the spore color patterns. There were many questions that were contemplated before beginning this experiment. To have an original frequency to compare our experiment to we needed to ask; what is the cross over frequency between spore colors in standard environmental conditions?
To actually formulate a result; what combinations of spore color frequencies would show that crossing-over occurred? The last question that was considered, and the most basic of them, was what are the challenges around actually performing this experiment? This is because the tan chromosomes and the black chromosomes would be kept separate, and so they would not mix and therefor create two rows, one solely black and one solely tan.
However, and meant that there was a crossover that occurred in the chromosomes, because some alleles coding for tan were mixed with some alleles coding for black when the chromosomes crossed over, thus the colors were mixed partially when the spores emerged.
To determine whether there is a change in crossover frequency, we compared the amount of recombinant asci fruiting body containing the asci to the amount of non-recombinant asci. They were placed in a pattern of four, so that each color is only adjacent to the other. This allowed them to grow and come in contact with one another, and form multiple different asci for examination.
After allowing the Sordaria to interact and grow for two weeks, an inoculating loop was used to scrape some of the Sordaria from the agar plate. The plates then were taped and allowed two weeks to grow. After two weeks, the samples had flourished.
We first scooped up small portions of each of our samples and put them on a slide with a drop of water, creating squashes, to be viewed under the microscope. When viewing under the microscope, each of the four group members counted and recorded their own twenty asci.
While recording, each member categorized whether the asci they found had represented type A, type B, or type C recombination type. Last, when each member had attained their individual data, we combined our data to create a total data for our entire group.
Then we proceeded to combine our data to find a section and a course total. Results Four separate sectors analyzed the data of this experiment, the individual, the group, the class, and the section. This means that on average there were 30 units between the cross over and the centromere of the chromosome. The fact that all of the map distances are around the same number also helps to represent the accuracy in our results.
Discussion After observation of the Sordaria fimicola, we were able to depict the different types of crossing over. This supports our hypothesis— crossing over did occur in the S. Because we were able to see that crossing over did occur and examine the three different cross over types, we can now say that sexual reproduction attributes to increases in genetic variation.
This example of the process of meiosis shows us that independent assortment and crossing over attributes to the variety of offspring that are produced in Sordaria fimicola. This large variety leads us to know natural selection plays a large role in the life cycle of fungus and especially S. There may have been replication of certain asci strands. The experiment, however, is still reliable due to the large number of spores counted.
This large number of gray spores and tan spores allowed for a reliable average to still be found. Future experiments may find this information useful because it gives insight into the how often crossing over occurs and therefore at what rate genetic variation is happening.
By knowing more about genetic variation rate, we can learn more about evolution and how that effects natural selection. Experimenters could use this information to compare the rate of genetic variation to the effects it has on natural selection. References Cyr, R. Heredity and the Life Cycle. In, Biology Basic concepts and biodiverity course website.
Written by Hass, C. Saleem, Muhammad. University of Haifa, Israel. Figures and Tables Table I. Of these twenty, twelve were recombinant meaning crossing over took place.
The other were not recombinant and therefore crossing over did not occur. Table II. Of the 40 gray spores counted, 24 were recombinant meaning crossing over took place while 16 were non-recombinant.
Of the 40 tan spores counted, 28 were recombinant while 12 were non-recombinant. Table III. Of the gray spores counted, were recombinant and crossing over took place while 92 were non-recombinant. Of the tan spores counted, were recombinant while 95 were non-recombinant.The study published in the Genetics Journal and referred to in the logy laboratory manual studied whether there is a natural genetic variation for recombination frequencies and whether it correlates to environmental conditions and adaptation. Before they are split, there is a phenomenon called recombination that occurs, where certain genes from nonsister chromatids will switch with the same genes from its partner. Of the tan spores counted, were recombinant while 95 were non-recombinant. The cross over frequency was Follick Biology H, Section 1 October 19, Title : Meiosis and Genetic Diversity in the model organism, Sordaria fimicola Introduction : Naturally occurring two mountain slopes with differing climatic conditions in Israel, such as the Evolution Canyon EC I located in Lower Nahal Oren, Mount Carmel, have become research models for understanding how environmental conditions influence evolutionary forces such as crossing over and thereby contribute to the survival of populations. There were many questions that were contemplated before beginning this experiment.
Error could have occurred while the smaller groups were compiling data into a whole class result. The squash was placed under a microscope for examination.
The other were not recombinant and therefore crossing over did not occur. In the asci strains in S.
Sordaria are good organisms to use for experiments like these because they are inexpensive, ethical, easy to see, and quick to reproduce. Discussion After observation of the Sordaria fimicola, we were able to depict the different types of crossing over. This supports our hypothesis— crossing over did occur in the S. Then we placed it onto a slide, preparing the squash by putting the Sordaria scraping into a drop of water and placing a coverslip overtop of it pg. Our group data Figure 3 has 28 asci with the combination, 14 asci with the combination, and 22 asci with the combination.
To answer this, one must observe the chromosome behavior during the sexual reproduction life cycle also known as meiosis. Patel 1 Riddhi Patel Dr. There is a type which happens when there is no recombination, and there are, for example, four gray spores and four black spores next to each other. The samples were then prepared by depositing them onto a small dot of water on the microscope slide with a coverslip over it, then they were observed under the microscope to determine the recombination pattern. Our
Before performing this experiment we hypothesized that we would be able to see that crossing over did indeed occur in the S.
Table II. Scientists gathered samples of the organism living on both slopes and analyzed the differences in crossing over and the differences in crossing over frequencies. Materials and Methods The crosses were set up by dividing an agar plate into fourths, and placing two pieces of black Sordaria strains alternating with two pieces of gray or tan Sordaria strains. Before performing this experiment we hypothesized that we would be able to see that crossing over did indeed occur in the S.
Results Four separate sectors analyzed the data of this experiment, the individual, the group, the class, and the section. This process is essential to life on earth. Related Papers. In, Biology Basic concepts and biodiversity course website. 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.
There are six different spore arrangements that can occur: 4 black: 4 tan and 4 tan: 4 black , 2 black: 2 tan: 2 black: 2 tan and 2 tan: 2 black: 2 tan: 2 black, 2 black: 4 tan: 2 black and 2 tan: 4 black: 2 tan. In, Biology Basic concepts and biodiverity course website. The specimens were grown in the laboratory, where wild type spores from these crosses were then self-crossed to create a second generation of wild type spores. This data will serve as Patel 2 a control group to which one can compare the cross over frequencies in strains on the two slopes to determine if the environmental conditions are the trigger for the difference.
This means that on average there were 30 units between the cross over and the centromere of the chromosome.
What are the Stoudt 2 frequencies of the two crossover types for each color strain? This large number of gray spores and tan spores allowed for a reliable average to still be found. The process of meiosis and crossing over is displayed in the pattern of the spores in the asci.
There are four research questions that we are trying to answer. To figure out that answer is why we performed this lab.
As you can see from Figure 2, the individual data contained 9 asci with the combination, 5 asci with the combination, and 6 asci with the combination. Saleem, Muhammad. Even though we had substantial support for our hypothesis in this experiment, there are always sources of error. Of these twenty, twelve were recombinant meaning crossing over took place. It is important as biologists to recognize what genetic recombination are caused by and how it affects the order of the spores.