A male mouse from a true-breeding strain of hyperactive ...

Question

A male mouse from a true-breeding strain of hyperactive animals is crossed with a female mouse from a true-breeding strain of lethargic animals. (These are both hypothetical strains.) All the progeny are lethargic. In the F₂ generation, all offspring are lethargic. What is the best genetic explanation for these observations? Propose a cross to test your explanation.

Accepted Answer

Hi everybody welcome back. The next question says which of the following statements about the true breeding line is false. So let's think about what a true breeding line is. As you can guess by the name, It means a line of animals that in which you always see this can depend on seeing the same trait appear reliably from parent to offspring over many generations. And let's recall, we're looking for a false statement here. So how do you obtain a true breeding line um by generating this inbred population so that over the generations as you have repeated inbred crosses, you have a whole line in which the individuals are nearly genetically identical to each other. So in a sense, they're almost clones, which is and they're very useful in genetic research. Since you have a population with a single trait you're studying and this population is being nearly genetically identical. You can depend upon them not to have variation affect your experiments due to other genetic effects. So we'll say nearly genetically identical. So let's look at our answer choices here. Choice A says they are inbred populations. Well, this is true. That's how you generate a true breeding line by many generations of inbreeding to create more and more and more similar individuals in all of their genes. So since this is true, this is not our answer, we're looking for a false statement. Choice B says they have the same specific not ipic trait and this is true. Um Usually in case of a true breeding line, you're looking for a line where you can reliably generate offspring um with a specific trait you're looking for and you want all the offspring to have that trait. So that's true and therefore not our answer. They are usually hetero sagas for the alleles associated with a specific trait. Well this is not true. This would be our false answer here. I'm gonna go ahead and highlight that. That's what we're looking for here. Because if an individual is hetero sickness for a trait, then half the time it's going to pass one alley onto its offspring and half the time it'll pass the other the other alley. So if we're looking for a line that's specific, that's reliably going to give us the trait we're looking for in all the offspring. You definitely wouldn't want the individuals to be heterocyclic as. Then you would only get that trait showing up in some of the offspring. Well, just for me to be thorough, go on to answer choice D. It says they're pairs of alleles that express a specific trait are the same. Well, this essentially means homos, I guess if you're a pair of allele is the same and for the same reason that choice C was a false statement that makes this statement true. Again, you want that gene passed on reliably you have nearly genetically identical individuals. So you want them to be homos, I guess for the trade of interest. So they only pass on that particularly since choice D. Is true. That's not our answer. So again, which of the following statements about the true breeding line is false choice. See they're usually hetero zegas for the alleles associated with a specific trait. See you in the next video.

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