Multifactorial Inheritance: Introduction

by Georgina Cornwall, PhD

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    00:00 Welcome back. As you’ve probably already ascertained, most genetic disorders are multifactorial in nature, having both an environmental and perhaps multiple genetic components or multiple environmental components. In this lecture, we’ll talk about ways that we start to sort out genes from variants and environment. There are definitely genetic components where we see complex interactions among a number of different genetic variations and even polygenic types of inheritance.

    00:43 Clearly, there’s also an environmental component or many environmental components.

    00:49 Each of us has a different experience in both realms including quite chance events that could happen even during development of a fetus in utero. Moving into looking at these different traits, we have two distinct types of traits that we can measure. First of all, we have discrete or qualitative traits in which you either express in edition or you do not. Phenylketonuria would be a great example.

    01:21 Either someone has it or they don’t, so qualitative, yes or no. Then we could have a quantitative trait.

    01:30 Usually, quantitative traits are something we could measure. For example in this figure, we have systolic blood pressure. It occurs over a continuum. We have people on the lower end and then a bell-shaped curve.

    01:47 We’re all quite familiar with this Gaussian type of distribution. We can compare people with certain mutations and those without the mutations and see some variants in the average blood pressure.

    02:00 Quantitative versus qualitative, we have either a spectrum or we have a yes or a no.

    02:09 There are different ways that we try to tease apart the genetics from the environment in order to establish the relative contributions of each. We know, sure, we know that relatives share more alleles than non-relatives. Briefly, we’ll cover that siblings generally share about 50% of their alleles.

    02:35 That’s average because it’s fairly random which parts that each got from a mother or a father.

    02:43 It could be quite a lot. So, you have one sibling that looks particularly like the mother or both siblings look particularly like the mother or the father. So we get a random mix. On average, 50% is shared which is definitely more than two unrelated individuals. Because of these familial similarities, we can use familial aggregation studies as well as correlation studies. Now, don’t worry too much about what those are yet. I will walk you through each of those. We can use those to determine the genetic contribution versus environmental contribution to some of these sort of mysteriously genetically predisposed conditions.

    About the Lecture

    The lecture Multifactorial Inheritance: Introduction by Georgina Cornwall, PhD is from the course Multifactorial Inheritance.

    Author of lecture Multifactorial Inheritance: Introduction

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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