Okay. So this question states that you have conducted a monohybrid cross, observing these F2 phenotypes in the cross. It appears you were crossing flowers, likely red or white, and the F2 generation ended with approximately 900 red and 300 white flowers. The question asks which of the following null hypotheses is best for using the Chi-Square Test. The Chi-Square Test is used to determine whether your expected values are the same as your observed values. In this cross, you obtained these offspring, with about 900 red and 300 white flowers. It's asking which of these ratios you expected for this cross, which one you want to test to see if the genetics are functioning accordingly.
A 9 to 3 ratio is what we're going to calculate and write it as a ratio. One of these ratios here must match a known genetic ratio - options are a 3 to 1 ratio, a 2 to 2 ratio, a 9 to 3 to 3 to 1 ratio, or a 3 to 2 ratio. If unsure, there's an obvious one, but we can eliminate some easily. We can discard the 9 to 3 to 3 to 1 because there aren't four phenotypes, only two (red and white), making this option untenable. The next we can discard is the 2 to 2 ratio, representing an equal distribution, which would mean either both phenotypes would be 900 or 300, but this is not what we observe. We see a 900 to 300 ratio, indicating they are not equal, so option b can't fit.
The remaining options are 3 to 1 and 3 to 2. The best approach here is simple division: if you divide 300 into 900, it fits 3 times. Thus, 300 times 3 equals 900, aligning with a 3 to 1 ratio. For the 3 to 2 ratio, we would expect a 900 to 600 ratio, which isn't observed. So, doing the math, dividing 300 by 900 yields 3. Thus, calculating 300 times 3 confirms it equals 900, establishing a 3 to 1 ratio.
Thus, the answer is A. If you observed this phenotype distribution, the null hypothesis that you would want to test is whether your values align with the expected values of a 3 to 1 ratio. With this conclusion, let's continue.
