Beyond Gregor Mendel

by Georgina Cornwall, PhD

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    In this lecture, we will continue our investigation of classical genetics by looking a little bit beyond Mendel. We will be looking at Mendelian inheritance patterns that don't quite exhibit the expected ratios. This isn’t that Mendel is wrong; they are just extensions of his concepts. By the end of this lecture, you will be able to predict the outcomes of mono and dihybrid crosses using probability methods as well as interpret test cross data to determine unknown phenotypes and finally you will be able to explain why not all crosses exhibit Mendel's predicted phenotypic outcomes. First let us begin by looking at probabilities. We can predict the outcome of test crosses using a much simpler method really than Punnett squares. Some of us get hooked on Punnett square, but realistically probability methods are a much more simple way to go about it. I don't know how much experience you've had with probability, but we will take a quick look at two rules. One is the rule of addition and one is the rule of multiplication. And these are rules that really allow us to turn sentences into mathematical equations. The rule of addition states that two mutually exclusive events, the probability of either event occuring is the sum of their two probabilities. Now that seems like a lot of words. Let us look at an example so that you can see what we mean exactly. Let us say you have one six sided dice and you want to roll that dice and get either a 1 or 2 or 3 or 5 or 6. Well you probably already have a pretty good idea that no matter what six sided dice you roll with six numbers on them, you are very likely to get one of those numbers as in...

    About the Lecture

    The lecture Beyond Gregor Mendel by Georgina Cornwall, PhD is from the course Understanding Genetics. It contains the following chapters:

    • The Rules of Addition and Multiplication
    • Predicting the Outcome of a Cross
    • Is It Homozygous or Heterozygous?
    • Polygenic and Pleiotropic Inheritance
    • Multiple Alleles and Incomplete Dominance
    • Phenotypes Affected by Environment and Epistasis

    Included Quiz Questions

    1. 1/4
    2. 1/2
    3. 1/8
    4. 3/4
    1. True
    2. False
    1. Pleiotropy : multiple genes affecting one phenotype
    2. Epistaxis : one gene masking the effect of another
    3. Multiple Alleles : more than two versions of the allele for a given trait
    4. Incomplete dominance : results in an intermediate phenotype that looks like blending but is not

    Author of lecture Beyond Gregor Mendel

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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