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Examining Mendelian Genetics Using Caenorhabditis Elegans And Cross Experimenting

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Introduction

In this experiment, we will be examining genetic inheritance and the transfer of traits such as performed in the experiment done by Gregor Mendel with his garden peas. However, unlike Mendel, we will be using Caenorhabditis elegans (C. elegans) nematodes instead of garden peas. C. elegans are worms measuring at around 1mm and consume E. coli and other microorganisms such as bacteria. They are useful in understanding biological functions especially ones found within humans. The worms have a very short life cycle, 3-5 days from when they are an embryo to when they grow into mature adults. In the experiment, we performed two genetic crosses between males and hermaphrodites C. elegans that either carry a wild type (+) or carry a dumpy mutation (dpy-3-), so as to examine the pattern of inheritance in accordance with Mendelian genetics. The hypothesis of this experiment is that the wild type (+) is dominant relative to the mutant dpy-3- (dumpy) and that the dpy-3- gene is located on the X- chromosome.

Before beginning the experiment, we needed to be equipped with the skills needed to properly use a dissecting microscope such as hand-eye coordination. We, the experimenters, needed to know how to be able to pick up the bacteria as well as the worms and then be able to transfer the worms safely into an empty Petri plate. This all must be done without killing the worm or scratching the agar plate. Also, it was crucial that we were familiar with the different parts of the dissecting microscope as well as their functions so as to ensure a successful genetic crossing. Another skill we needed in this label is to be able to distinguish between hermaphrodites and males. To do this, we examine the tails of the worms. Hermaphrodites have tapered tail, while males have a very blunt tail. Also, being able to identify the wild type worms versus the dumpy is important. Wild type worms usually are longer in length, then dumpy, which tend to be shorter and fatter. Lastly, it was important to practice sterilization, so we needed to learn to flame the wireworm pick after each use.

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After the group members were confident that we had the necessary skills to perform the experiment, we began with our first monohybrid cross of the C. elegans. Using the platinum wireworm pick, one member transferred 2 dpy-3-/- and 2 him-8-/- homozygous hermaphrodites to the plate with 4-6 him8 males. It was important to flame the pick after each use transfer of worms to the plate so as to practice proper sterilization techniques. We checked to see how we did under the dissecting microscope and then wrapped the plate in plastic wrap making sure to label the plate F1 generation, group number, class section, and the professor’s name. We then handed the plate to the instructor to properly store for a week in the incubator at 15 °C. After a week, we then performed our second cross and transferred two F1 L4 stage hermaphrodites to a seeded agar plate, wrapped the plate in plastic wrap, labeled F2 generation, group number, class section, and the professor’s name. We handed the plate to the instructor to properly store for a week in the incubator at 15 °C. After a week had passed, the group then used the dissecting microscope to organized the worms based on gender, male or hermaphrodite, and phenotype, wild type or dumpy. This data was recorded onto a table.

Discussion

After performing a chi-square analysis of our data, we found the p-value to be less than 0.05, which indicates that there is around a 5% chance both observed and expected data are merely a coincidence. In this case, we must reject the hypothesis since the p-value indicates that the observed data and the expected data are significantly different. While completing our chi-square analysis, we also noticed the ratio between F2 worms with the wild type and dumpy phenotypes has failed to match the 3:1 ratio seen in Mendel’s monohybrid cross experiment. Therefore we can not make a determination on which phenotype is the dominant or recessive allele, thus rejecting our hypothesis that the wild type (+) is dominant relative to the mutant dpy-3- (dumpy) and that the dpy-3- gene is located on the X- chromosome.

Conclusion

In all, we have rejected our hypothesis. The proportion of wild type and dumpy observed have failed to equal to Mendel’s 3:1 ratio of a monohybrid cross. Our p-value was less than .05 signaling that our observed and expected data are significantly different. Possible errors that may have occurred throughout the experiment could possibly be due to our identification skills of wild type males and hermaphrodites as well as dumpy male and hermaphrodites. Experimenters may have mistaken a wild type phenotype for a dumpy phenotype and vice versa. This error could have seriously tainted our results and make it appear as though the proportion of wild type worms to dumpy worms was not 3:1. Another error could be miscounting or losing count while organizing the worms into gender and phenotype. Improvements must be made so as to avoid these types of errors. Prior to beginning the experiment, experimenters must be well versed in how to work with the dissecting microscope including how to pick up bacteria without scratching the agar plate as well as picking up worms without killing them because this can affect our results after we cross the worms twice. Also, it is vital that there are multiple experimenters who can work efficiently with the dissecting microscope as well as multiple experimenters who can quickly and accurately identify C. elegans gender and phenotype. The organization of the worms based on gender and phenotype should be divided amongst experimenters so as to prevent one experimenter, who may not be well equipped in distinguishing the worms, from doing all the separation of C. elegans into gender and phenotype.

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Examining Mendelian Genetics Using Caenorhabditis Elegans And Cross Experimenting. (2022, February 24). Edubirdie. Retrieved January 31, 2023, from https://edubirdie.com/examples/examining-mendelian-genetics-using-caenorhabditis-elegans-and-cross-experimenting/
“Examining Mendelian Genetics Using Caenorhabditis Elegans And Cross Experimenting.” Edubirdie, 24 Feb. 2022, edubirdie.com/examples/examining-mendelian-genetics-using-caenorhabditis-elegans-and-cross-experimenting/
Examining Mendelian Genetics Using Caenorhabditis Elegans And Cross Experimenting. [online]. Available at: <https://edubirdie.com/examples/examining-mendelian-genetics-using-caenorhabditis-elegans-and-cross-experimenting/> [Accessed 31 Jan. 2023].
Examining Mendelian Genetics Using Caenorhabditis Elegans And Cross Experimenting [Internet]. Edubirdie. 2022 Feb 24 [cited 2023 Jan 31]. Available from: https://edubirdie.com/examples/examining-mendelian-genetics-using-caenorhabditis-elegans-and-cross-experimenting/
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