#T01 Geneticists usually study differences between people

How DNA is organised in your cells. Image by: Eukaryote_DNA.svg

Vivre la différence!

I remember my professor saying that the science of genetics would not exist if all humans had the same genetic information.

These days, we measure genetic information in terms of the pairs of bases that make up the double stranded DNA molecules.

What is DNA and why does it matter?

DNA is a chemical found within chromosomes, in each of our cells.

There is an identical copy of the DNA in each cell.  It was brought together when your father’s sperm fertilised your mother’s egg.

There are 3 billion pairs of DNA bases in each of your reproductive cells, organised into 23 chromosomes.

There are twice as many pairs of DNA bases in the other cells of your body. This because you receive DNA from you father (through his sperm) and your mother (in her egg).

These cells have 46 chromosomes, made up of 23 pairs.

Most of the DNA bases are the same in everyone. This should not surprise us.

DNA helps the cells to produce the proteins needed to keep us alive.

Our bodies work in much the same way, so we would expect the DNA bases involved in keeping us alive to be the same, too.

Geneticists can only study the 3 million DNA base pairs that differ between us. This is only 0.001% of the total number of base pairs.

Between and within

When geneticists say that a characteristic like height is about 75% genetic and 25% environmental, they are talking about differences in height between individuals in a population.

(In this case, a sample of adult females from Finland.)

They are NOT talking about the relative importance of genes and the environment in the development of your individual height.

The emerging science of epigenetics now allows scientists to study changes in how our cells use our DNA across our lifetimes.

They still study differences, but this time they are changes that occur within us as we grow and develop.

Studies like this are important, but they are relatively new.

So, our first tool for clear thinking is that:

#T01 ‘geneticists usually study differences between people and not within them.’ 

We always need to check exactly what geneticists are talking about, when they present their evidence and we must not confuse ‘between’ and ‘within’.