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3. Extensions to Mendelian Inheritance

Penetrance and Expressivity



Penetrance and Expressivity

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Hi in this video we're gonna be talking about penetrates and expressivity. So um organisms sometimes have a genotype that doesn't completely match the phenotype. So it would be kind of like if they had a little that said they were supposed to be you know purple it was dominant but they weren't quite as purple as you were expecting them to be. Or maybe they're not even purple at all. And so why would this happen? Well, sometimes environmental factors can mask the phenotype. Sometimes other interacting genes either through episode Asus or modifiers or suppressors will actually, you know, cause that phenotype to not be expressed. Or maybe the phenotype is subtle. It's very difficult to observe. But in any of these cases this is when you have a genotype or an allele with a certain phenotype but it's not quite that phenotype. So there's two ways to describe this penetrates is the percentage of individuals with a given alil who exhibit the phenotype. And expressivity is when the degree it measures the degree to which a given alil is expressed. So for instance, brown fur can have different intensities. It can be dark brown, it can be light brown and it can be all the different ranges of brown in between. So that's expressivity. So we want to look at this. This is gonna be penetrates. So there's a certain percentage of these. So three out of five are presenting the red phenotype where two of them aren't. And so penetrates is going to measure the percentage of those that are actually expressing the phenotype that they have the genotype for expressivity On the other hand, measures the degree to which it's expressed. So we're looking at this red, this is going to be completely expressed and this is going to be barely expressed. And there's all these different ranges in between. So this actually measures that range where penetrates measures whether or not it's actually being expressed. So with that let's not move on.

A group of individuals exhibit a range of intermediate phenotype between dominant and recessive. What term measures this phenotype?


Penetrance measures which of the following?