Lab 03 - DNA extraction and PCR of the PV92 Alu insertion locus

Lab 03 had been cancelled due to the power outage and building evacuation that we had on Thursday of week 2. It was meant to be the lab to introduce students to the Polymerase Chain Reaction (PCR). We did it today.

We extracted DNA from our cheek cells and used it to set up basic PCRs.

Our target in the PCR is the PV92 Alu insertion locus, located on chromosome 16.

Alu elements are a family of short interspersed repetitive elements (SINEs) that have mobilized throughout primate genomes for the last 65 My, by retrotransposition.

There are more than 500,000 Alu elements per haploid genome in humans (about 5% of our genome). Depending on the insertion point they may be associated with some genetic diseases (e.g. some cases of hemophilia, familial hypercholesterolemia, severe combined immune deficiency, or neurofibromatosis type 1). But in most cases it has no effect on the individual's health.

Some Alu insertions are very recent and polymorphic. The most recent are human specific (HS) and such is the case of PV92. Because the PV92 insertion locus is HS, polymorphic, neutral (invisible for natural selection), and easy to detect, it has been widely used in human genetic population studies, and it has been one of the markers used to support the out-of-Africa hypothesis.

In this lab we will test the presence of 0, 1, or 2 PV92 Alu insertions in our genomes, and most likely will use them for a short population genetics exercise.

The following picture illustrates the possible outcomes of our PCRs:

The sample on lane 1 belongs to an individual with no PV92 Alu insertion, lane 2 to an individual with insertion in both chromosomes, and lane 3 to an individual with an insertion in one chromosome.

What is your genotype like?

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Lab 12 - pGLO Small Scale Plasmid Purification Lab 13 - pGLO Restriction Enzyme Digestion (RED)

pGLO plasmid and restriction map
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Today we used the bacteria we transformed with the pGLO plasmid and cloned a few weeks ago to perform a small scale plasmid DNA purification (minipreps) and isolate the pGLO plasmid again.

Then we performed a restriction enzyme digestion, RED, using the restriction enzymes EcoRI and HindIII (see restriction map).

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Exam 2

Today we had our second partial exam.

Stats:

(click image for full size view)

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Lecture, chapter 10 - Transcriptional gene regulation in eukaryotes

We finished covering chapter 10, on transcriptional gene regulation in eukaryotes. We devoted special attention to gene silencing via formation of heterochromatin, a process in which histone acetylation and cytosine methylation are key processes.

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Lab 11 - Polyacrylamide Gel Electrophoreses (PAGEs)

Friday, October 23, 2009

Today we did a new kind of electrophoresis, or you could say that we did two. Polyacrylamide Gel Electrophoresis (PAGE) is a process that uses the same principle of agarose gel electrophoresis, but it uses a polyacrylamide gel, a thinner, more expensive kind of gel that provides a higher resolution than its agarose counterpart.

Specifically we used it to run protein samples and we did it in two ways. We ran a native gel, in which the proteins migrate at different rates depending on their size (molecular weight), tertiary structure, and charge. We also ran a denaturing gel, in which the proteins are denatured with high temperature and kept denatured by SDS contained in the electrophoresis buffer, so their rate of migration through the gel depends exclusively on size.

The goal was to estimate the size of the green fluorescent protein (GFP) by comparing its migration through each gel with the migration of a molecular weight ruler (a "protein ladder") loaded onto the same gel.

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