PCR Forensics

Personalized Genetics



Adaptive Evolution


TAQ Polymerase

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In this module, students will analyze their own DNA for variation associated with several traits:


Muscle Performance

rs1815739 (C or T)

Wouldn’t it be great to be able to look at your DNA and decide which kinds of sports you are better suited for?  Then you would know whether to try out for the 50 meter dash or the marathon.

We aren’t quite there yet but we are making some progress.  One of the more interesting genes to look at is ACTN3.  It has the instructions for a protein that goes by the same name, ACTN3, that is only turned on in fast-twitch muscle fibers.  These are the kind of muscles used in power sports like sprinting and weightlifting.

So if you have a version (or allele) of this gene that makes a protein that does its job well, you may want to be a sprinter.  But if your gene makes an ACTN3 protein that doesn’t work as well as it could, then you might want to go for long distance running.

The C allele makes a protein that works, the T allele makes one that doesn’t work.  Do you think power athletes are more likely to have a C allele or an T allele? 

If you guessed C, you are right.  Both CC and CT are more prevalent in power athletes while TT are more common in endurance athletes.  This makes sense since TT people don’t make any ACTN3 protein that works.

Now we’ll check what your ACTN3 gene looks like.


Lactose Tolerance

rs4988235 (C or T)

About half of Asians and Native American become lactose intolerant around two years old. By the time they are 6 years old, 80% of Asians and Native Americans are lactose intolerant and that number rises to over 90% by the time they are 10 years old. About 80% of African Americans and Hispanics are lactose intolerant as adults.

But, there is a lot of variation in people with European ancestors. Only about 3% of people from Scandinavia and 8% of white Americans are lactose intolerant. In some parts of southern Europe as many as 70% of adults are lactose intolerant. Overall, many people with European ancestors can drink milk. These people are lactose intolerant because they can no longer digest a sugar in milk called, you guessed it, lactose.

Of course most of these folks could drink milk when they were kids.  And 25% of adults (mostly those of northern European descent) can still drink milk.  So what is going on?

Lactose is digested by an enzyme in our small intestines called lactase.  The instructions for making lactase are found in the lactase gene.  Most adults become lactose intolerant because their lactase gene shuts off later in life.  When it shuts off is different for different people. 

Most of the 25% of adults who can drink milk have a DNA difference near their lactase gene that keeps it from being shut off.  This is why these people are said to be lactase persistent. 

Most people are GG at this allele…their lactase gene shuts off at some point during adulthood.  Those who can keep drinking milk are usually either AG or AA. 

The A allele is not the only way to be lactose tolerant, it is just the most common form in Europeans…it is very rare in Asians and Africans.  Another allele that leads to lactase persistence is pretty common in a small group of Africans.  It affects the lactase gene similarly but does so in a different way.

Now let’s see if you are AA, AG, or GG here.  Remember, even if you are GG you still might be able to drink milk because you either have a different allele that allows it or your lactase gene hasn’t shut off quite yet.  Remember that different people lose their ability to drink milk at different ages. 




rs16845098        T (human) vs C (Neandertal) 

Until recently, there was no evidence that humans and Neanderthals had kids together.  This is no longer true.  Now it looks like lots of people in Asia and Europe (but not Africa) had Neanderthal ancestors.
Scientists figured this out by sequencing the DNA in old Neanderthal bones and comparing what they found to various modern human DNA.  They noticed that Neanderthals, Asians and Europeans shared some DNA that Africans did not.  See the video at https://www.23andme.com/you/gen101/videos/anc02/ to see why this makes sense.

Today we are going to look at one allele that is shared by humans and Neanderthals.  If you are XX or XY, then you probably got the X from a distant ancestor.  If you are YY, then you are pure Homo sapiens at this allele.

Of course, you could still have Neanderthal ancestors if you are YY.  There are lots of other alleles shared by Neanderthals and humans that we didn’t look at today.

More info about Neandertals at The Tech Museum.


Photic Sneeze

rs10427255 (C or T)

Around 25% of people sneeze when they look into a bright light or go out into the sun.  Lots of these people also sneeze when they breathe in cold air or something strongly minty.  No one is sure why but there is some interesting speculation here: http://genetics.thetech.org/ask/ask239

Scientists have found an allele that is associated with photic sneeze.  People who are CC have a slightly higher chance of sneezing when they go out into the sun, CT people have typical odds and TT people have a slightly lower chance of sneezing when they go in the sun.  Another way to say this is that for every c you have, you are about 1.3 times more likely to have photic sneeze reflex.  Is this reflex dominant, recessive or incompletely dominant?




SNP presentation is a powerpoint presentation to introduce this topic to the class.

Informed consent for for the students to sign before making their own DNA.

Genotyping protocols has the PCR protocol, a table showing the expected PCR sizes, and a figure showing PCR results.

SNP worksheet is a worksheet for the students to perform for this module.

SNP Primer list is a list of the primers, and some PCR conditions.