PCR is a common technique used to amplify specific regions of DNA. Put more simply, its a process that allows us to create copies of a piece of DNA. There are two main properties of PCR that we take advantage of - amplification (getting many copies) and isolation (of a single region).

If you understand the basic idea of photocopying, then you can understand PCR.

I should note that the role of PCR has changed over time and I will mostly be focusing on the current use. Additionally, there are several variants based off the standard PCR, including rt/qPCR, but those will be covered in a different post.

Why do a PCR?

Typically PCR is just a step to let us do something else with a gene or region of DNA. It is the first step in gene cloning or for things like gene editing. It can also be used ‘genotype’ an individual for a gene, i.e. figure out which specific copy of a gene someone has.

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The goal of gene cloning is to get a single copy of the gene from an animal and into an archive. The rest is just the individual steps necessary to do this. Cloning genes allows us to easily and consistently retrieve the exact same copy and to share it between labs or even organisms.

Step		Description	Biology Jargon
1		Get a copy of the gene from the animal	PCR
2		Put the gene in an archival format	Ligation into a plasmid
3		Make backup copies or archive it	Bacterial transformation
4		Confirm that the copies match the original	Sequence the insert
5		Retrieve a copy to use	Miniprep

What is a vector and what how is it used?

A vector is a small, self contained piece of DNA that can be added to an organism, typically bacteria. It is how we archive the gene we are cloning.

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We are constantly seeing both news articles as well as scientific publications on new genes - the new gene for intelligence, cancer or happiness. So lets start at the beginning by figuring out what a gene is. Simply, its a way to refer to inherited traits.

When a gene is identified as playing a role in a trait, this can be caused by basically two things - 1) different versions of a gene called an allele or 2) changes in how or where a gene is used. To understand how genes can give rise to different traits, we need to first understand how a gene functions.

Thus, lets look at how, in the simplest case, a trait like the color of a flower, can arise from a gene.

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All of biology functions around the core of DNA, RNA and Proteins or the so called Central Dogma of Molecular Biology. The key here is that you always go in the order of DNA→RNA→protein. You can’t jump from DNA to protein or visa versa; it just doesn’t happen. However, you don’t have to go all the way. Just because you made RNA doesn’t automatically mean it will be a protein. This is also not necessarily a one-to-one relationship. One RNA can be used to make several copies of the exact same protein.

Why do I care?

Because a gene can be looked at in each step of the DNA→RNA→protein progression. We look at all the different steps because how a gene is functioning can be regulated or changed at any point. However, in all cases, we are still interested in the gene.

Biological Levels are also explained through the analogy of a book.

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