Imagine an instruction manual for how to build every part of your body, but instead of an alphabet of 26 letters you only have 4. The instructions are in your DNA and the alphabet are the DNA base pairs adenine, cytosine, guanine, and thymine, or just A, C, G, T when abbreviated. Different combinations of these go on to form all your genes; think of them like sentences in the instruction manual. So instead of a sentence like 'you will have blue eyes,' you'll get something that looks more like ATTTGAGCATTAAGTGTCAAGTTCTGCAC. Genes are also huge! They're usually comprised of thousands of these bases.
Instruction manuals have chapters to better organise their information, and likewise you have chromosomes to organise your DNA. Humans have 46 chromosomes (23 pairs), and everyone inherits 1 set of 23 from each of their parents. The work to produce a copy of this instruction manual was called The Human Genome Project and was completed in 2003. This treasure trove of information has since been used for medicinal research, the understanding of disease and of human evolution.
In my current work, I've been screening different durum wheat plants for genes useful to farmers; so I've been looking for sentences like 'you will have yellower semolina,' or 'you will be resistant to pathogens.' This enables faster selection of improved varieties and works towards increasing the potential yield. I say potential yield, as there will be interactions with the environment that may limit this; like pests, frost or drought, so even though a plant may have amazing genes, it might not perform at its best. This is the difference between its genotype (the theoretical version that exists according to the instruction manual) and its phenotype (how the results of the instruction manual interacts with the world).
You exist today as a result of how your genes have interacted with your environment since before you were born. Your DNA is more than just a fixed blueprint for life though, and genes can be regulated in response to changing circumstances to help an organism thrive. This is called epigenetics and I'll write more about that topic in future.
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