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Autosomal Recessive Inheritance

by Georgina Cornwall, PhD
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    In this lecture, we’ll be visiting both autosomal recessive inheritance and then autosomal dominant inheritance. First, we’ll cover the recessive inheritance. Now, autosomal recessive diseases occur in individuals who have two mutant alleles. You’re probably familiar with that. Usually, autosomal recessive diseases are loss of function diseases. On occasion or regularly in the heterozygote, there’s some compensation. They may have half the gene product but in the case of sickle cell for example, you will have compensation. The individual is carrying the sickle cell allele, half of their hemoglobin will be of the sickle cell variety. Half of it will be of the regular variety. This is enough to get by. So, that’s what we mean by compensation. Having two recessive alleles in that case is fatal. But it’s not always fatal. It’s just the recessive condition expressing the actual phenotype. In these types of matings, we end up having unaffected individuals, carrier individuals. You can see both the son and daughter in the middle. Affected individuals, usually ¼ will be affected in a mating between two heterozygotes. Let’s take a look at three possible matings. First of all, you could have both heterozygous parents as we just saw in the last graphic. Here in the Punnett square, we can see that we result in indeed ¼ affected individuals. Now, we don’t have enough offspring like Mendel did with peas to really consider that ¼ of the offspring would have this. So, if we’re dealing with 1,000 pea plants, that’s one thing. But as individuals or parents, maybe we’re lucky to have four. You may see that one in four is affected. We call it a ¼ probability that you would have an affected child. We can work with probabilities because there’s also a ¼ possibility of a son. Anyway,...

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


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    Author of lecture Autosomal Recessive Inheritance

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD


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