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

Question

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

Given your conclusions in part (a), indicate the genotype of the following individuals: II-1, II-6, II-9 If more than one possibility applies, list all possibilities. Use the symbols A and a for the genotypes.

Accepted Answer

Hi everyone. Let's look at our next problem. It says examine the pedigree and determine the disorder under investigation. So we have a three generation pedigree here with four different genetic diseases. As our four answer choices. So let's look at this pedigree first and see what it's characteristic of. And then we can try and match it with one of these. So the first thing we notice is we see that we have a skipped generation here and that also we don't see when we look at the affected individuals on our pedigree, not all affected individuals have an affected parent. So not all affected individuals have affected parent. So this indicates to us that we're looking for a recessive disorder. Uh if it's a dominant disorder, um every affected individual have a affected parent since having the gene means you express the trait. And of course skip generations are characteristic of recessive disorders since parents can be carriers without being affected by the disease. So we settle on recessive and if we go down to our our answer choices, we can go ahead and rule some out choice B. Huntington's disease. Huntington's disease is an autism, all dominant pattern of inheritance. And in choice D. Fragile X. Syndrome, fragile X is an excellent dominant disorder. Um It's carried on the X chromosome and having only one copy um means that you're affected by the disorder. So even females can be affected by this. Unlike many excellent traits that are recessive where only males are affected so we can eliminate Huntington's disease and fragile X syndrome because both have a dominant pattern of inheritance. So let's go back to our chart. We just now have to look at our remaining choices are cystic fibrosis and hemophilia. Both are recessive, which is what we're looking for. Cystic fibrosis fibrosis is an autism. All pattern of inheritance on one of the autism's hemophilia is an excellent trait on the X chromosome. So let's look at our pedigree to see um which this would be. Well, our first big clue is that on this pedigree only males are affected. There are no affected females. And that's going to be our strong clue that we have an excellent trait here. Um When you have recessive X linked traits, it's very, very rare in females because females would have to inherit one copy from each parent as opposed to males. Since they only have a single X chromosome, they only need to inherit one copy, even if it's a recessive disorder, since they've only got one X chromosome. So we have no affected females. So that gives us that pretty strong hint right away. Um, and back up uh evidence for this. We see um no male to male transmission here. Um This affected male here in generation one Did not pass the disorder to his son. We don't see that. Um and these two affected males in Generation three did not inherit from their father. And in addition, we see in generation one generation to this affected male has three Children. His son is none of his Children are affected. His son does not pass it on as you wouldn't expect because if it's excellent uh son cannot inherit from a father. But we see in generation two there are two females, both of whom have affected sons. So both daughters of the original um affected male are carriers of the condition. So you have to female carriers. So all of these things add together to say that we have an excellent recessive disorder. And so we're going to eliminate cystic fibrosis, which is an autism away recessive disorder. And our answer will be choice C hemophilia, which is excellent and recessive as our pedigree indicates. See you in the next video.

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

Given your conclusions in part (a), indicate the genotype of the following individuals: II-1, II-6, II-9 If more than one possibility applies, list all possibilities. Use the symbols A and a for the genotypes.

Key Concepts

Pedigree Analysis

Dominant and Recessive Alleles

Genotype Determination from Phenotype

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