Hello I was wondering if someone can assist me in understanding these problems,

Question

Hello I was wondering if someone can assist me in understanding these problems, I do not expect you to actually draw a punnet square because it is impossible to do so on a computer, but if you could some what explain your methods it would be greatly appreciated.


1. Suppose that you purchased a well-shaped white summer squash plant and wished to use its seeds in a breeding experiment. However, you do not know its genotype. Describe a breeding experiment (referred to as a testcross) that you could carry out to determine the genotype of your white squash? (Hint: a testcross is usually performed between a known genotype and an unknown genotype.)

2. In summer squash, white fruit color (W) is dominant over yellow fruit color (w). If a squash plant homozygous for white is crossed with a plant homozygous for yellow, what will the phenotypic and genotypic ratios be for:
1. the F1 generation?
2. the F2 generation?


3. In roses, red petal color is dominant over white. Use R for the red gene. Use r for the white gene. If we cross two heterozygous red roses, use a Punnet square to describe the phenotypes and genotypes of the offspring.

Thanks Zack.

Explanation / Answer

I'll talk about 2 and 3 first, as they will help in understanding how to approach 1: 2. First for any Punnett square problem, write out the two genotypes that you're dealing with. For this case, you have homozygous white (WW) and homozygous yellow. Now, write a square like this: WW w w For each box in the square, just take the alleles from the corresponding row or column. So in this case, all four offspring will have the genotype Ww. Since white is dominant, all four will be white. This is the first generation. For the next generation, the square will be set up: W w W w So the four offspring will have genotypes: WW, Ww, Ww, and ww. Note the three will be white, and one will be yellow. 3. This question is identical to part 2 of the question above, except instead of Ww and Ww, you'll have Rr and Rr. But the conclusions are the same! So, for the first question, we want to cross the unknown squash with a squash of known genotype. Suppose we choose the heterozygous Ww one, then our table looks like: W w X x So the offspring will have genotype: WX, wX, Wx, and xw. Thus, depending on what X and x are (either W or w), we would expect to see different genotypes (and in some cases, phenotypes) for the offspring. Hope this helps!

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