In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? When designed matings cannot be conducted in an organism (for example, in humans), how do we learn that genes are linked, and how do we map them?

Video transcript

Hi everyone, welcome back, let's look at the next problem here. It says two genes are linked on the same chromosome. If they are inherited together blank of the time, We have choices of more than 50%, less than 50%, more than 10% or less than 10%. And I kind of think through this problem, let's imagine the case of a hetero. So we're going to be looking at this individual here for two genes who is the offspring of a cross between a Hamasaki is dominant and recessive parent. So we're saying that in this case this parent had only one type of gamete, which is big B. Little E. So that is the only type of gamete they could pass on and this other parent can only pass on little B little E. So in this case our individual that we're looking at this hetero sex individual inherited Big B. And biggie together little B. And little E. Together those were how they inherited from their parents. So now let's imagine two different scenarios, let's imagine our hetero six individual. In a situation where genes B and E. Are on separate genes. So they are not linked together at all. I mean separate chromosomes, excuse me, they're not linked together at all and they independently assort. So in this case, what kind of gametes can this hetero saiget produce? Well, they could produce the homos I guess dominant big being little biggie together just as that dominant parent had or little B. And little league together, just as the recessive parent had or they could independently assort. So they could have a big B from one parent and a little leaf from another. The little bee from one parent and biggie from another. In that case where there's complete independent assortment that gene is on two separate chromosomes. 50% of these gametes have the alleles inherited together because this home is I guess dominant and recessive gametes have inherited together. The alleles from the same parent. So complete independent assortment is. 50% of the gametes have the genes inherited together just by chance. Random chance. So now let's imagine this scenario, the opposite scenario where the two genes are linked so closely they're so close together in the same chromosome that you never have any recombination, they are always inherited together. Well, in this theoretical case of complete linkage. So here we draw the two chromosomes inherited and this hetero I get from their parents, you've got big b. And big e. Close together on the same chromosome, little be literally on the other parental chromosome. In this case of the gametes have alleles inherited together. So we see here this individual can only produce two types of gametes Hamas. I guess dominant Hamas, I guess recessive because there's no recombination. So now when we think about what happens if there's some linkage, there's some recombination but not a lot. You're going to be between 50% and 100%, being completely separate, 100% being completely linked. So two genes are linked on the same chromosome. If they're inherited together, Choice a more than 50% of the time. Again, 50% would be that minimum amount of gametes, um, that where the allies are inherited together just by random chance. So anything greater than 50% all the way up to 100% shows some sort of linkage. The genes are together on the same chromosome. They might be quite far if they're close to 50%, they might be quite far apart and recombined quite frequently. Um, but anything greater than 50% shows that two genes are linked on the same chromosome. So choice a more than 50% is our answer here. Thanks for watching. See you in the next video.