Crash Course in Genetics: Is it all in the DNA?

If you’ve been following this post series, you definitely will have noticed that I’ve talked a lot about DNA. So what is this post about?

You may recall from this post on the crisis in genetics that our standard definition of a gene has come under serious scrutiny as a simple DNA makes RNA makes proteins makes cell. Instead we defined it as follows:

“A gene is a section of DNA or sections of DNA that are split up. Each of these sections codes for an RNA chain that can transfer the information or a protein. These sections are controlled by and can control other genetic regulatory networks (GRNs), a term that encompasses processes that affect when and which genes are expressed and how they are (in other words, genes can turn other genes on and off and affect how they function). When genes do this, they can affect an individual’s phenotype, the combination of observed factors, such as height, skin colour, other features, etc…”

So this post is going to expand on the fact that only 1-2% of our DNA actually directly codes for protein and the rest was considered to be junk …. until fairly recently.

Every single cell in your body contains exactly the same genes, yet cells are dramatically different. A red blood cell is only 8 um wide, while a skin cell is 30 um and a neuron cell body is often over 100 um wide with several hundred dendrites sticking out! White blood cells can move themselves and sperm and egg cells are different again. Yet all of these contain exactly the same DNA. This leads to the obvious conclusion that only some DNA acts in a certain cell type and different DNA in others. The non-protein-coding genes perform these ‘regulatory’ functions, signalling different protein-coding DNA to act at different types or under certain conditions.

According to a recent widespread human genome project called ENCODE (ENCyclopaedia  Of DNA Elements) that is studying these gene interactions apart from protein coding, between 9-20% of human DNA has a regulatory function. They also concluded that an entire 80% of the 3 billion DNA base pairs can be assigned some form of biochemical function (if you’re interested, you can read the full-text Nature article here).

Certain genes (such as the Hox genes) act almost solely during the first days and weeks of embryonic development to signal differentiation of body parts, ie. the formation of a gastric opening and then appendage (arms, legs, etc..) development. Other important regulatory genes include the Sry gene in mouse studies which regulates the production of a certain protein (called SOX9) that can result in the formation of female rather than male genitals even when the animal in question has an X and a Y chromosome.

Other such interactions are plentiful and clearly demonstrate the sheer complexity and brilliance of the human genome … concepts that are challenging current evolutionary theories, a topic to be addressed next week!

 

If you found this article interesting, perhaps considering reading the other posts in this series:

What is a gene?

The crisis in genetics

Inheritance

Genotype vs. Phenotype

 


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