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Lecture 17

Lecture 17- Extensions of Mendelian Genetics I

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University of Toronto St. George
Human Biology
Christian Campbell

Tuesday, March 10, 2009 -The focus of todays lecture is on extensions of Mendelian Genetics the idea of taking Mendel to a whole other level where we can actually explain what it is that we see in terms of the variation in the world around us and how its inherited. -Lets take stock of where weve been so far: -In Lecture 14, we looked at Mendels simple traits, this simple mode of inheritance, and looking at the alternate forms of traits the dominant and recessive modes of inheritance. We saw that these antagonistic pairs were inherited in stereotypical ratios that were predictable using math. These same traits were applied when we looked at traits in humans. So if we looked at how traits were inherited in humans, the same basic probabilities for inheritance of traits that showed simple autosomal dominant or recessive modes of inheritance and we looked at how one would track that by using pedigrees. -Obviously, all traits arent that simple. If we look at the world around us, we see plenty of variat io n that cant be ac com mo dated by these simple Mendelian ratios & dominant & recessive modes of inheritance. So how do we explain the true variation that we see within a species? How do we reconcile what we know about the extent of apparent genetic diversity in the world around us with the model that Mendel proposed? -Today, were going to talk about wrinkles on Mendels laws and well see that the same laws are still there but bc of phenomena like dominance and co-dominance, pleiotropy, variable expressivity, etc., well see changes in the stereotypical ratios at least what we observe phenotypically. -Well also talk about environmental influence which is related to phenocopy and this will take us to the next level of understanding which will be related to information well later see in Lecture 22 and 24. -In other words, how do we reconcile our basic understanding of molecular genetics with the true variation we see in the world around us and how that variation gets inherited? -We know this on the basis of gene expression. We might have variable levels of effect based on variable levels of gene activity at a given locus.
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