X-linked Recessive Inheritance

by Georgina Cornwall, PhD

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    Here’s a question. Just to make it a little bit more interesting as we dig a little deeper. If a grandfather had hemophilia and the grandmother wasn’t a carrier or anything, could that hemophilia appear in descendants of his sons? Try to wrap your head around that. I know it looks like one of those exam questions, word problems and such. But let’s take a look at it. First of all, draw yourself out upon its square. Let’s put the grandfather across the top and the grandmother down the side. We call the grandfather as affected. So he’s X, little h, and a Y. The grandmother is not affected and not a carrier. So ,she has X big H, X big H. Go ahead and take a moment to fill it out. Let’s see what we come up with. See if you can answer the question. Would his grandsons be affected? Alright, so as we fill this out, we noticed that all of his sons would not even be carrying the recessive allele. Thus, it’s not possible even for him to pass on the disorder to any of his male progeny or grandsons. Of course, the grandsons could perhaps pick up an allele elsewhere and pass it on in future generations. But in his grandsons, we’re not going to see it travel through the paternal line. It has to go through a female carrier. We just examined this cross. You can see clearly that all females will be carriers and all males are unaffected. What about a different case? Now, we have a male parent that is not a carrier or not affected and we have a female that is a carrier. We can see that we have a one-to-one-to-one ratio. I challenge you now before we reveal what the...

    About the Lecture

    The lecture X-linked Recessive Inheritance by Georgina Cornwall, PhD is from the course Single-Gene Disorders.

    Author of lecture X-linked Recessive Inheritance

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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