Tetrad analysis is also a valuable tool in determining the genotypes of certain phenotypes, as well as linkage between two genes. If linkage is occurring between genes then the NPD is very rare to see compared to the PD and TT. If linkage is not occurring then the ratios of PD:NPD:TT are roughly 1:1:4. Once linkage has been determined and the ratios have been confirmed, it is easy to determine which phenotype is PD, NPD, or TT and simply match it to the correct genotype.
Mutations can be located at several different locations on a gene. Despite being able to be located at several different points on a gene, different mutations can lead to the same phenotype. Sometimes mutations occur at the same location of a gene, so when two organisms with the same mutation mate the mutation persists to the next generation. Sometimes two organisms will display the same mutated phenotype but will have mutations at different locations from one another. When mated together, the offspring of these two organisms will no longer display the mutated phenotype, resulting in a process called complementation.
Mutations can occur at several locations on a gene yet result in the same phenotype. Yeast are a good organism to study the heritability of mutations because of their small size, easy and quick growth, and easily definable phenotypes. These factors also make yeast good for using tetrad analysis to determine genotypes. To study this, several crosses were carried out on adenine deficient agar plates to see what haploid gametes and what diploid cells could survive without adenine present. It was found that HA0 is the only haploid yeast cell that can grow without adenine, while HA1, HA2, and HB1 cannot grow without adenine. HB1xHA0 and HB1xHA2 were able to grow without adenine present, while HB1xHA1 and HA1xHA2 were unable to grow without adenine present. These results occurred because of the locations of the mutations on the gene, resulting in dominant alleles, mutation matches, complementation, and non-mating. A tetrad analysis was then taken of HB1xHA2. The results of the analysis show that there is a roughly 1PD:4TT, with three unknown tetrads due to culture deaths. While the analysis showed the correct ratio of PD:TT, it cannot be confirmed if the genes are linked or not due to the undefined tetrads.
Mutations can occur at several locations on a gene yet result in the same phenotype. Yeast are a good organism to study the heritability of mutations because of their small size, easy and quick growth, and easily definable phenotypes. These factors also make yeast good for using tetrad analysis to determine genotypes. To study this, several crosses were carried out on adenine deficient agar plates to see what haploid gametes and what diploid cells could survive without adenine present. It was found that HA0 is the only haploid yeast cell that can grow without adenine, while HA1, HA2, and HB1 cannot grow without adenine. HB1xHA0 and HB1xHA2 were able to grow without adenine present, while HB1xHA1 and HA1xHA2 were unable to grow without adenine present. These results occurred because of the locations of the mutations on the gene, resulting in dominant alleles, mutation matches, complementation, and non-mating. A tetrad analysis was then taken of HB1xHA2. The results of the analysis show that there is a roughly 1PD:4TT, with three unknown tetrads due to culture deaths. While the analysis showed the correct ratio of PD:TT, it cannot be confirmed if the genes are linked or not due to the undefined tetrads.
Plants sense gravity using statoliths in their roots. By cutting a cross section of the root and staining them, the researchers found that statoliths are present in adventitious root nodes no matter the age of the node. In order to study the variable of gravity when it came to the adventitious root growth, they used different experiments. First, they used a clinostat experiment, where the plants were planted and mounted and rotated for three days. After the rotation, the rotated stems had a root angle of 106°, as opposed non rotated stems which had an angle of 120.4°. The stems that were being rotated were unable to feel a constant directional effect of gravity, while the non rotated stems did, which means that gravity had a 14.4° change on the root angle.
Yeast were plated and each plate was mutagenized by Dr. Loomis by exposing the plate to UV radiation for 9 seconds via a UV light box. Cells that turned red were allowed to grow into larger colonies to be used for the experiment. Four different mutant strains were produced, two of mating type A and two of mating type alpha. Yeast labelled “A” were of the A mating type, while yeast labelled “B” were of the alpha mating type. A YED plate was set up in a grid to perform crosses (Figure 2). Each side consisted of one mating type of non-mutant yeast (HA0/HB0), a known Ade1 mutant (HA1/HB1), a known Ade2 mutant (HA2/HB2), and the two mutant strains for that mating type (MA1/2, MB1/2). After one day of growth, the yeast were crossed in a gridwise manner. Two days later, the yeast were replica plated to an MV plate and an MV+Adenine plate (Figure 3). After three additional days of incubation, the yeast colonies were observed. The full procedures followed for all steps can be found on Moodle.
Yeast were plated and each plate was mutagenized by Dr. Loomis by exposing the plate to UV radiation for 9 seconds via a UV light box. Cells that turned red were allowed to grow into larger colonies to be used for the experiment. Four different mutant strains were produced, two of mating type A and two of mating type alpha. Yeast labelled “A” are of the A mating type, while yeast labelled “B” are of the alpha mating type. A YED plate was set up in a grid to perform crosses (Figure 2). Each side consisted of one mating type of non-mutant yeast (HA0/HB0), a known Ade1 mutant (HA1/HB1), a known Ade2 mutant (HA2/HB2), and the two mutant strains for that mating type (MA1/2, MB1/2). After one day of growth, the yeast were crossed gridwise. Two days later, the yeast were replica plated to an MV plate and an MV+Adenine plate (Figure 3). After three additional days of incubation, the yeast colonies were observed. The full procedures followed for all steps can be found on Moodle.
Interestingly, a plant that was exposed to white light and ethylene for two days and then grew in darkness for two days. In the case of this plant, its roots initially grew downwards for the first two days, and then they grew upwards for the next two days, giving the roots a kinked shape by the end of the four days. Similar to that, a plant grown in darkness for two days and then white light for two days grew upwards for the first two days and downwards for the final two days. This created a kinked shape in the roots, however it was in the opposite direction. Upon researching the effects of gravity on the growth of the roots, they found that gravity affected the root growth in a less impactful way.
In addition to red light, they tested the effects of blue light on the plants. Blue light is received by phototropins in plants. Phototropins are in control of stomatal opening and chloroplast movement. When the rice stems were exposed to the blue light, it had a dosage dependent pattern. At a low fluence rate of blue light, the rice stems had similar root growth and angle to rice stems that were grown in the dark. In comparison, at a high fluence rate of blue light, the rice stems had similar root growth and angle to stems that were grown in white light. The direction of rice roots growth in response to white light was found to be reversible. They studied four different rice plants in different setups; one plant was exposed to white light and ethylene for four days, and it grew roots that went downwards. The next plant was grown in darkness, and its roots grew upwards.
After my observations, I found that my results were conclusive to my hypothesis. My results of the experiment showed that the pre-pasteurized NA plates contained lots of growth. Large colonies that seemed to be clumped together made it difficult to distinguish and count colonies, yet there seemed to have been one isolated colony present on the plate. The organisms appeared to have a dull texture with an opaque color, and slight elevation. As for the post-pasteurized plate, there was growth present. There was a lack of colonies present in comparison to the pre-pasteurized plate.
Both plates expressed similar colony morphology. Each colony that presented growth on the plate was isolated thus making counting possible. The organisms also presented an opaque color and very dull texture, with slight elevation. When observing the post-pasteurized organisms under the phase contrast microscope, the organisms were bacillus shaped in a chain-like arrangement with lots of movement. Tiny black dots within cells presented endospore formation, however no germination was detected. The post-pasteurized organisms that were gram stained and viewed under the light microscope at a total magnification of 1000x, expressed a streptobacillus arrangement of organisms with distinct purple color indicating that the organisms were gram positive.
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