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Lecture 17

Lecture 17- Extensions of Mendelian Genetics I


Human Biology
Course Code
Christian Campbell

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Tuesday, March 10, 2009
-The focus of today’s 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 it’s inherited.
-Let’s take stock of where we’ve been so far:
-In Lecture 14, we looked at Mendel’s 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 variation that cant be accommodated 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, we’re going to talk about ‘wrinkles’ on Mendel’s laws and we’ll
see that the same laws are still there but b/c of phenomena like
dominance and co-dominance, pleiotropy, variable expressivity, etc.,
well see changes in the stereotypical ratios at least what we observe
-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 we’ll 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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