What we measure and why?

This analysis was performed using R (ver. 3.1.0).

Molecular basis of phenotypic variation

Genomics is widely used in scientific and clinical research to make discoveries and to develop diagnostic tools. One of the uses of these technologies is to try to explain the molecular basis for phenotypic variation. For example, why cancer cells live longer than normal cells? And why are some cancer cells susceptible to treatment, while others are not?

One of the explanation for these phenotypic differences must come from the genome. DNA is transcribed into a message (RNA), and this message is translated into proteins. Changes in the amount and in the structure of these molecules can explain phenotypic variation. This is why we want to use these technologies to answer these questions.

DNA: chromosomes, SNPs and other variants

DNA is the molecule where genetic information is stored. DNA is empaquetted in chromosomes and stored in the nucleus. Every cell in our body has an exact copy of these chromosomes with the same information. Most of our cells have two alleles for each chromosome. And the exception are the sperm and egg that only have one.

Biologists have measured the DNA of many individuals and have noticed that, although 99.9% of their genome is identical. There are places where they see differences. And they’ll see a proportion of the population with one variant and the rest with another. These sites, their current estimates are in the millions, are called SNPs, and you will many times see two versions of the two possible bases at the site. This is why there’s so much variabilty between humans.

These variants are common in humans. And biologists today are trying to find if some of these SNPs can be used to explain phenotypic variation, like, for example, disease. There are some technologies to measure these SNPs for millions of sites at the same time.

Gene expression

Different cell types have the same DNA so how are they so different? How is a liver cell so different from a neuron? How is a neuron so different from a colon cell?

One of the reasons this happens is because different genes are expressed. Genes are a small segments of DNA coding for protein.



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