Albinism in humans is inherited as a simple recessive trait. F...

Question

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

Construct a pedigree of the families in (b) and (c). Assume that one of the normal children in (b) and one of the albino children in (c) become the parents of eight children. Add these children to the pedigree, predicting their phenotypes (normal or albino).

Accepted Answer

Hi everyone, Welcome back. Let's look at our next problem. It says, determine which the following pedigrees exhibits autism or recessive inheritance for a particular trait. Well let's before we look to our pedigrees, let's recall from our content videos. What kind of pattern would we expect to show um to demonstrate autism or recessive inheritance in a pedigree? Well, for autism, all inheritance, we'd expect to see no difference in male versus female inheritance. So we'd expect to see roughly equal numbers of males and females inherit the trait um versus a sex linked trait. In particular. If we had an excellent trait, you would see no male to male transmission, no male could pass an excellent trait on to his son and then recess the patterns that we expect to see for recessive inheritance, we'd expect too often see skipping of generations since um unaffected individuals can be carriers without having the disease. So not carriers generations versus when we have autism will dominant inheritance, we would expect to see every individual, every affected individual having an affected parent. Because if you inherit even one alley, all of a dominant trait you express that trait. But in recessive inheritance we'd expect to see generations being skipped. So let's look on at our first pedigree here. Well, as we look at pedigree a, we see there is no skipping, all three generations have affected individuals. And when we look at these affected individuals, we see that every single one of them has an affected parent. So this is more characteristic of a dominant trait. Um We can already eliminated because of that. Since we're looking for recessive. Um We can also see that we have both males and females being affected with both male and female parents. Uh So we don't expect that to be sex linked, but we obviously could eliminate already since it's showing a dominant pattern. So let's move on to pedigree B. Again. Same thing. We see no skipping and we see are affected individuals here have all at least one affected parent. So this also looks like a dominant pattern of inheritance. Again that's enough to eliminate it. But if we wanted to eliminate in particular excellent trait, we see here from generation 1-2, we have an affected male parent with an affected son. So we know it's not an excellent trait. So now I'm just gonna scroll downward so we can see our remaining two pedigrees here. Let's look at choice. See so here in choice C while we do see we only have one affected individual in the entire pedigree. Um It did skip Um generations here, we have no affected individuals and generations one or Renect an individual just in Generation two. So we have definitely a recessive pattern of inheritance here, I'm not going to immediately select it as my correct answer, I'm gonna mark it as a possibility just because if we wanted to rule out a sex linked trait since we wanted to show autism a recessive. Um We only have one affected male here, of course excellent traits are gonna appear more often in males. Um This affected male did not pass on the trait to a son. So um we want to look and see whether uh if choice D. Shows a better example that's definitely not sex linked, we might choose that instead. So let's move on to choice D. And see what that looks like before we choose C. As our answer. So looking at choice D. Um We see affected individuals in all three generations. So there's no skipping. And as we highlight our affected individuals we see that they all have at least one affected parent. So again characteristic of dominant inheritance rather than recessive. And if we needed to eliminate sex linked we see male to male transmission from generations 12 generations to. But we can already be eliminate D. For showing a very clear pattern characteristic of dominant inheritance. So that since that leaves us with only one pedigree that indicates um a pattern of recessive inheritance will go ahead and select choice C. For answer. Um It is important to know just in case we had other possibilities. Um Or just other types of questions that a pattern like you C. N. C. Could also be due to a spontaneous mutation arising in the affected individual and generation two. But given that our questions asking us um for a pattern of recessive inheritance and we don't have a choice of none of the above. We don't have a choice of other possibilities were pretty safe selecting choice C as our answer for the pedigree showing an example of autism. Well, recessive inheritance. See you in the next video.

Key Concepts

Recessive Inheritance

Genotype vs. Phenotype

Pedigree Analysis

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