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13. Mendelian Genetics

Test Crosses

13. Mendelian Genetics

Test Crosses

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concept

Test Crosses

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in this video, we're going to begin our lesson on test crosses. And so what you may have noticed from our previous lesson videos is that FINA types do not always reveal the Gina type. And so, for example, we could have a yellow P. But we don't necessarily know just from looking at that yellow p if that yellow P has a Homo zegas dominant Gina type with two dominant Leal's to capital wise, or if that yellow P has a hetero zegas genotype with Onley, one dominant illegal and one recess of illegal. And so once again, just because we know the phenotype is yellow does not mean we know what the Gina type is. It could either be homos, I guess, dominant or heterocyclic. And so the question is, how do scientists determine what the Gina type is in a scenario like this one? Well, in some cases, scientists can use what are known as test crosses to test or identify the Gina type of an unknown mystery parent with an unknown Gina type. And so the way that test crosses work is that the mystery parents Gina type can be identified by cross fertilizing, cross fertilization with a known homo zegas Recess if Gina type. And so, if we take a look at our image down below notice on the left, we're showing you a mystery parent who you can see. We have a detective here trying to figure out what is the Gina type of this mystery parent. We have a yellow pea plant or yellow piece, but we want to determine what is their genotype. Is it homo zegas dominant, or is it hetero? Zegas? And again, we don't know which one of these two it would be. So this is why this is the mystery parent. And we can take this mystery parent and cross this mystery parent with a known parent. A parent who's Gina type we know is homo Xigris recessive to lower case wise, which would create these Greenpeace here. And so you can see this little light bulb here saying, I know because this parent has the known Gina type. And so when you cross the mystery parent with the known parent who is home a zegas recessive that will reveal the Gina type of the mystery parent and we'll be able to talk about exactly how that will work and exactly how test crosses work in our next video. So I'll see you guys in that video

2

concept

Steps to Performing a Test Cross

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in this video, we're going to talk about the steps to performing a test cross. And so let's say that we have a yellow pea plant, but we're not sure what the Gina type is of this yellow pea plant. Maybe this yellow pea plant has a homeless, I guess. Dominant Gina type. But maybe this yellow plant has a hetero zegas Gina type. How do we figure that out? Well, we need to perform a test cross. And so there are really three steps when it comes to performing a test cross and notice that Step three also has a part three a and three beat. And so the very first step in performing a test crosses to cross the mystery parent with the unknown Gina type with a homo zegas recess it parent. Then the second step of performing a test cross is to analyze the babies of the cross or, in other words, to analyze the offspring FINA types and then the third and final step of performing the test crosses to make a conclusion about the mystery parents Gina type. Based on the results, if all of the babies or all of the offspring had the dominant phenotype, then that means that the mystery parents genotype must be home, a zegas dominant or to capital wise. But if the offspring of the cross showed mixed offspring with mixed FINA types, then that must mean that the mystery parents Gina type is hetero zegas, meaning it has one dominant alil and one lower case or recess of Alil. And so let's take a look at our example down below to see how this test cross exactly works to determine the Gina type of this mystery parent, this yellow p. And so notice that over here on the left hand side and on the right hand side, we're showing you this mystery parent. And of course, we know that it is yellow, but we don't know what it's Gina type is. We know that it has at least one dominant alil, but is it going to be homeless, I guess Dominant or hetero? Zegas? Well, what we need to do is the very first step, again is to cross the mystery parent with the homeless, I guess, recess of Parent and so notice that in both situations we're taking the mystery parent and we're crossing the mystery parent with a Hamas, I guess. Recess, if, parent. And then what we need to do is analyze the results of the babies. If all of the babies come out 100% with the dominant phenotype of yellow, then that must mean if we trace this, uh, backwards to see the possible results of the offspring, we know that they must have at least one dominant Aaliyah, one capital. Why? And that must mean that the gammy must have had a capital y here as well. And that must mean that the mystery parent is Homo Zegas dominant. And so if all of the offspring 100% of the offspring show the dominant phenotype that they're yellow piece as we sit here, all dominant offspring means that the mystery parents Gina type is Homo zegas dominant to capitalize. But let's say that there is a mixture of FINA types in the offspring where 50% of the offspring are showing the dominant trait of yellow piece. But the other 50% of the offspring are showing the recess Ivo trait for Greenpeace. Then of course, that must mean that half of these, uh, here must be, um homo zegas recessive having to lower case wise. And, of course, they must have gotten this lower case. Why from one of the fathers game it's. And that means that the mystery parent must have a home hetero six genotype. And so again, if you see mixed offspring, that means that the mystery parents genotype is hetero zegas. And so you can see that just by analyzing the results, do we see mixed offspring or do we see ah, 100% dominant? Uh, the 100% of the offspring showing the dominant tree and depending on that well, you either figure out that the mystery parent was home a zegas dominant or if there was a mixed that the mystery parent is hetero zegas. And that's how you determine the Gina type of the mystery parent by performing a test cross. And so this year concludes our introduction to how to perform a test cross, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video

3

Problem

Problem

A single gene test cross is conducted to determine the genotype of a pea plant that shows the dominant phenotype for height (T = tall, t = short). If all offspring of the cross show the dominant phenotype, then the genotype of the unknown parent is _______.
a) TT.
b) tT.
c) Tt.
d) tt.

A

TT.

B

tT.

C

Tt.

D

tt.

4

Problem

Problem

You want to determine the pea color genotype of a pea plant with yellow peas. You conduct a test cross with your mystery pea plant. The test cross results in 50% of the offspring possessing yellow peas and 50% of the offspring possessing green peas. What is the genotype for pea color of the mystery parent?
a) YY.
b) Yy.
c) yy.
d) None of the above.

A

YY.

B

Yy.

C

yy.

D

None of the above.

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Additional resources for Test Crosses

PRACTICE PROBLEMS AND ACTIVITIES (8)