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Lab- Dihybrid Crosses Essay

This lab was about corn genetics- dihybrid crosses. We had to analyze the corn kernels and later on see if our hypothesis was either supported or rejected. We wanted to discover what color and coat texture was dominant (purple and wrinkled, yellow and wrinkled, purple and smooth or yellow and smooth). I had not yet done labs like these ones, but I definitely had studied about monohybrid and dihybrid, crosses. Also, I have done many activities on this aspect and other labs that were similar but not identical to this one.

To perform this lab, we had to click on the corns that were purple and smooth, yellow and smooth, purple and wrinkled or yellow and wrinkled. Then, we analyzed the data we had collected and plugged it in the Chi Square to support or reject or hypothesis. This lab was of quite simple procedure and did not require many steps.

My calculations were my Chi-Square tests, which I am posting here under the discussion box.

In this lab, I counted the kernels in corn based in color and coat texture. In the hybrid crosses the purple and smooth showed up the most (later on we can see these are the dominant alleles when we plug these values in the Chi-Square test table). If we were to do Punnett Squares (parents of hybrid crosses and two heterozygous parents) to discover the estimation of the outcomes (the percentage of chance the outcome will be a certain thing), we would see that expectations are that purple and smooth alleles will cover 9/16 of the corn and that there is 9/16 probability that the kernel will end up being purple and smooth. With the Punnett Square, we can see that purple and wrinkled alleles have 3/16 chance of occurring, just as yellow and smooth alleles.

The yellow and wrinkled alleles are 1/16 probable to occur. With these numbers we can come up with the expected ratio for this cross, which is 9:3:3:1. However, the actual numbers may vary a bit from this ratio, or even vary a lot, since these probabilities are just chances, and there are still chances, even though they are small, that the opposite of the expected may happen (which is why there is the 0.5 margin of error that
we use in order to calculate a more precise Chi-Square value). Now lets move on to the Back cross, in which one of the parents is heterozygous and the other is homozygous recessive. We can also to a Punnett Square for this case. In this situation, there would be an equal chance and equal probability of each one of the possibilities to occur, thus, giving us a ratio of 1:1:1:1. Of course, we do not live in a perfect world, and therefore our crosses wont always appear in this ratio, since even though they are small chances there are chances of having alleles appearing more significantly or more times than others, which is why there is a margin of error. Here are my Chi- Square tests:

In the hybrid cross, we could see that there were more purple and smooth kernels. We can also see in the Chi Square test, that the closer the observed value is from the expected value, the smaller the chi-square value for that color/coat texture and vice versa. The final value for the Back cross was so small because the observed numbers were already a bit similar to the expected numbers. However, we couldn’t yet confirm the hypothesis because it could be just the recessive allele occurring more times than the dominant. To confirm, we had to plug in the values on the Chi Squared test table. If our values were accepted (which happened, the values were extremely below the maximum value), we could confirm our hypothesis.

However, if our values were rejected, because they were too different from the estimated, we wouldn’t be able to confirm our hypothesis (if we had hypothesized on which was the dominant allele based on the bigger number of kernels present on the corn from a specific color or coat, and these numbers caused the Chi Squared test to reject our value, we would know that the results were different from the expected (probably we had even hypothesized wrong since we had based ourselves on the number of kernels of a specific coat/color while they could even be the recessive allele) and that there wasn’t necessarily a mistake or problem while measuring the data, but just the improbable happening: having the recessive allele appearing more than the dominant, even though there was only a small chance of that happening).

Of course, sometimes there are errors in our graphs and in measurements that cause the chi-square to reject our values, which in this case would be truly wrong. My graphs represent direct relation because as the number of kernels of each color/coat increased, the respective graph also increases. I did meet my purpose since I could discover the correct hypothesis by seeing how many kernels of each coat/color there was on the corn and applying this information into the Chi Squared test.

My data supports my hypothesis since with my graphs and tables (Chi Squared test), I can see that the Purple and Smooth are the dominant alleles. There aren’t many sources of error, but we could have measured the number of kernel for each respective color/coat wrongly, which would definitely affect the final value. I did not find any space for improvement in this experiment1 Conclusion: This should be in the form of a testable statement or statements Select the hypothesis you verified and restate it here. OR, if you did not verify your hypothesis, state a hypothesis that is supported by your data.

Since, I supported my hypothesis, I am restating it here: Purple and smooth alleles are dominant for color and coat texture in corn. Reflection: Personal commentary about what you learned from the lab activity. I really liked this lab and I feel like I have learned a lot from it. Since we had already used Chi Square before in the last lab, it was easier this time. However, this time we wet further and we really learned more about hybrid crossing, this time focusing on dihybrid crossing. I really liked this lab, but I thought that clicking on every single corn was very tiring!

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