BIOL 202 Lecture Notes - Lecture 11: Environmental Noise, Twin Study, Heritability

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7 Feb 2013

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In the conferences, TA's bring their own problems in addition to the problem sets, to give insight
into the kind of problems we will be faced with.
Should be done problem set 3
Quantitative traits, (polygenic or continuously varying traits)
trying to understand the underlying genetic basis of these kind of traits....difficult cuz under
influence of multiple genes, hard to tease apart, also, there is environmental noise interrupting this.
In order for a trait to respond, there has to be some contribution of the gene (heritability) to the
Only when you have heritable variation that you can see some kind of response to selection.
Important to know if theres underlying heritable basis. If a disease is genetic, maybe we can target
that gene for therapeutic purposes. (important both in agriculture and in medicine)
If you have a population wt a lot of variation (ex: bristles on drosophila) you can select upwards or
downwards from 36 bristles relatively easily, theres not much heritable variation at some point. The
dotted line, the population reverted back a little bit, then jumped back up, because
1) could be mutations that have increased variance for bristle number
2) could be recombinations, recombining with other genes (hadnt run out of variation for
bristle number...recombination can mix up that variation)
have genes all over the genome that affect the gene of interest. (deleterious=???)
Heritability in the broad sense is
2 ways to get it. We cant clone humans, but humans come close to cloning themselves. The
heritability of political conservatism is slightlyl heritable (?)..
In twin studies, having twins isnt sufficient . You need twins that have been separated at birth and
raised in different environments to study.
The 3 height graphs show something. (recall heritability =Vg/Vx....a correlation value could be
equal to this, in the textbook this is shown)
you can only get broad sense heritability of twins when you have separated them at birth. You get
phenotypic correlation in environments if they are not separated, otherwise, you can't tell if
environment or gene type is responsible for this. Also adoption isnt perfectly good, because twins
often get adopted into similar environments
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