Mendel crossed peas having round green seeds with peas having wri...

Question

Mendel crossed peas having round green seeds with peas having wrinkled yellow seeds. All F₁ plants had seeds that were round and yellow. Predict the results of testcrossing these F₁ plants.

Accepted Answer

everyone. Let's look at our next problem it says. And doing a test cross the genotyping question is crossed with a blank genotype, let's recall what we what and how. We use a test cross. Um We're looking at genotyping questions. We have an individual unknown genotype and we use the test cross to determine the genotype of this individual whose phenotype expresses the dominant trait. Trying to figure out are they homicide or hetero. Six for the dominant. Aaliyah. Let's look at our answer choices, noting that choice. D. S. All options are correct. There could be more than one correct answer. Well, to give us the best information in the test cross, looking at the offspring to determine the genotype of the unknown parent. We'd want to cross it with a parent who was homeless. I guess recessive, they can only pass on the recessive gene letting you look at the offspring to determine whether that parent is home was I guess dominant and can only give a dominant gene or whether their heads. And to just look at this a little more clearly, let's look at the two punnett squares. Um From those two possibilities. So we'll just put up two pendant squares where we've imagined. Here's our test cross parent that we're going to use. Homocide is recessive and we have these two possibilities for the genotype in question. So if this unknown parent is Hamas. I guess dominant. We're just calling this dream be. Well of course, see that the offspring are 100% expressing the dominant phenotype. Whereas if our unknown genotype parent is Hatteras Vegas Half our offspring will express the dominant trait, half the offspring will express the recessive trait will see that 1-1 ratio of dominant to recessive phenotype. So looking at that offspring gives us a good way to check and determine the genotype of the unknown parent. Just to be thorough. Let's look at our other answer choices. Since we do have that choice. A. D. Choice A says homocide is dominant. Well if our unknown genotype expressing this dominant phenotype is crossed with a homogeneous dominant parent, this parent can only pass on the dominant gene, meaning that all of the offspring will have the dominant gene and therefore express the dominant phenotype. So that doesn't give us any information. So not at all useful as a test cross. That also means we can eliminate choice D. All options are correct. When we look at choice B. It's not quite so clear. So we'll just put up a punnett square to understand why that had arisen Vegas um parent would not be as useful and test cross as a home as I guess recessive parent. And first we'll think of a scenario where we have a genotype in question which is homos I guess dominant crossed in a test cross with a heterodox parent. Well, since our homes I guess dominant parent only donates a dominant gene. Just like with our other test cross example we'd see 100% of the offspring showing the dominant genotype. Now let's look at a punnett square and imagine if we have a hetero sickos parent crossed with a hetero ziggy's parent in a test cross, Well then we're going to see a 3-1 ratio where we're going to see 75% of the offspring expected to show the dominant phenotype, While 25% are expected to show the recessive phenotype. Well, when we think about a single test cross in the offspring, If we're looking for only 25% to have show that recessive trait, you're far more likely just by chance not to have any recessive offspring, even if the parent unknown parent is ahead of us as compared to a cross with a homesickness recessive parent where you expect that offspring to a ratio of half and half. So that's why the head of a parent is not as useful a test across. So we're gonna go and eliminate that since we know we can't have multiple correct answers anyway and settle on choice. C in doing a test cross, the genotyping question is crossed with a homocide recessive genotype. See you in the next video

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Mendel crossed peas having round green seeds with peas having wrinkled yellow seeds. All F₁ plants had seeds that were round and yellow. Predict the results of testcrossing these F₁ plants.