Consider the three pedigrees below, all involving a single human ...

Question

Consider the three pedigrees below, all involving a single human trait. For each combination that you excluded, indicate the single individual in generation II (e.g., II-1, II-2) that was most instrumental in your decision to exclude it. If none were excluded, answer 'none apply.'

Pedigree chart illustrating inheritance patterns of a single human trait across generations.

Accepted Answer

Hello. Everyone here's our next problem in the following pedigree. First identify the inheritance of the autism. All trade being studied and then determine the Jenna types of person three in generation three and person four, generation too assume a little a big a to be dominant over a little for the trait being studied in the pedigree first, I'm gonna scroll down so we can see our answer choices along with our pedigree. So for our first job is to identify the inheritance of the autism trait. Now we're told it's an autism traits. So we don't need to worry about figuring out whether we're talking about autism versus sex linked. But we want to determine whether this is a dominant or recessive pattern of inheritance. So the first thing we can notice um very obviously when we look at this pedigree is that we have skipped generations, We have affected individuals and generations two and 4 but no affected individuals in one or three. And in addition the affected individuals in our pedigree don't have affected parents. When you have a dominant pattern of inheritance, you expect that every affected individual will have an affected parent. Since you only need one copy of the illegal to show the trait and therefore having inherited that copy from a parent, the parent must also be affected. So this combination of skip generations and affected individuals that don't have affected parents leads us to conclude that this is a recessive trait we're studying. So with that in mind our question asked us to spot the jena types of Person three in Generation three and person two in generation four. So that would be this unaffected male in generation three and this affected female in generation four. Well let's start with the easy one. The affected female. Since we're talking about a recessive trait then we know that any affected individual must have the genotype little a little A. So we can go ahead and look at our answer choices and eliminate choice A. Which has that second person as being big A big A. But that would be unaffected. And we can eliminate choice C. Which shows that person is having a genotype of big a little A. Since that would make them a carrier and not affected by the treat. So we're left with choices B. And D. So now let's turn our attention to person three in Generation three. Well we know this person has had a child who is affected and that affected child must have inherited one recessive gene, one recessive value from each parent. So both parents in this case individuals three and four must have one little A. Both parents are also unaffected by the trait. So they must be hetero ziggy's carriers so they must be big a little A. So now we know our genotype of our second person person three in generation three. They must be big a little A. When we look at our answer choices, we see that choice be is the correct answer here with that correctly labeled choice D. Has person three in generation three being a little a little A. But if that were the case they would be affected with the treat. Now one last little interesting. Side note here is when we look at this pedigree that affected individual in generation four is the offspring um of parents who are first cousins. And indeed both parents are carriers of the trait um which they inherited most likely from a carrier in generation one. Um Who would have passed on the gene to the affected person generation to um the father and uncle of those parents. And so this tree kind of illustrates how um when there are closely related parents it is more likely to pass on a recessive trait such as this one. But back to our problem again the pedigrees or the jena types of person three and generation three person two in generation four or Choice B. First one being big a little A. The second being little a little a. See you in the next video

Consider the three pedigrees below, all involving a single human trait. For each combination that you excluded, indicate the single individual in generation II (e.g., II-1, II-2) that was most instrumental in your decision to exclude it. If none were excluded, answer 'none apply.'

Key Concepts

Pedigree Analysis

Dominant and Recessive Traits

Genetic Exclusion

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