What exactly does it mean to have 'good' genes... or 'bad' genes for that matter? And why do people say 'it's all in the genes!' when someone beats cancer or wins a marathon? In fact, what the heck is a gene?
Since Gregor Mendel (1822-1884) started playing in his garden with pea plants, the concept of the gene was born. It all began when Mendel recognized that the colour of a plant's flower was directly linked to the colour of its parents- a simple observation that changed how we understand all living things. Today we take it for granted that we will look like our parents. We accept that we inherit our parents' attributes. Well, this is because we inherit their genes- both the 'good' and the 'bad'.
Actually, what we inherit from our parents is their DNA, and it is the DNA that contains the genes. You can learn more about DNA in the upcoming post "you and your genome". Essentially, DNA is a very long string of letters (nucleic acids) that make up words (genes). It is in every single cell of our body, and it is how each cell uses the DNA that determines how the cell behaves.And what does that mean - how a cell uses DNA? Well, DNA is like a script, it is like a book that is filled with information. In order to use DNA the cell must decode the script, it must read the book. A cell reads DNA just like we do: by reading one word, and then another word, and another, until we have all the information we need. Genes are the words in the book of DNA; genes are the bits of information.
The information encoded by a gene is translated into a protein, and each gene makes a different protein. There are thousands of different proteins that make up our cells- proteins are the building blocks of our bodies. If a cell is like a city than proteins are the workers in the city. In every city we have bankers, builders, policemen, politicians, protestors (if there is a G20 summit in town), factory workers, etc.... each of these people have their own job and function in the city. Similarly, each protein in the cell plays a different role and each protein does its job to ensure the cell runs properly. Proteins are encoded by genes. When the cell reads DNA and uses a gene (called 'gene expression') it does so by making a protein, and it is the protein that will do the work. This is the primary function of a gene.
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These are just a few of the proteins that genes encode for. Each of these proteins has a very specific and unique sequence of amino acids that results in a specific and unique shape and function. |
Now that we have covered the basic concept of a gene, lets consider how a gene can help or hurt us. Although generally every cell in our body contains the same DNA, sometimes there are minor changes (called genetic mutations) in the DNA that can drastically affect the gene, and thus affect how the cell behaves. This is because very slight difference in genes can result in huge differences in proteins, which can in turn change how the protein does it's job. If the activity of a protein changes than the behaviour of the cell can change, and this can result in changes in how we behave.
Lets return to our 'book of words' analogy. We all know what words are, we use them every single day. A word is a sound used to describe something specific. Each word is different because it sounds different and this allows us to name or describe different things. The slightest difference in a word can result in a huge change in its meaning (take 'pot' and 'lot', for instance). Well, genes are the exact same way. Each gene has a unique and specific 'sound' which results in a unique and specific 'meaning'. The 'sound' of the gene is based on the DNA, and the 'meaning' of the gene is based on the protein it encodes.
Just like the letters in a word will determine its meaning, the letters in a gene will determine the type of protein it makes. This is because proteins are made from 'amino acids' (which are 20 chemicals that our body gets, or makes, when we metabolize our food) and the letters that make up a gene encode for a very specific set of amino acids, that make a very specific protein. So if there is a change in the letters of a gene there will be a change in the amino acids of the protein, which results in a change in the function of the protein. If the change is bad (a 'deleterious mutation') than it may result in the protein not being able to do its job anymore, and this can cause a huge problem for the cell (just think about the disruption a strike can cause in a city). On the other hand, if a change is good (called a 'beneficial mutation') than it can improve how the protein does it's job, which may give us some kind of advantage. These slight differences in our genes is what makes some genes 'good' and others 'bad'. For instance, if we have a mutation in a gene that results in a protein using energy more efficiently than we may be able to run faster and win a marathon. It is the sum of all these differences that make all of us individuals and that make each of us who we are.
In short, the DNA we inherit from our parents encodes for genes that in turn make proteins. Sometimes there are very slight differences in our genes which result in differences in the proteins our cells make. These slight differences in proteins lead to differences in us. Some of these differences are good (like a gene variation that makes someone run faster) and some of these differences are bad (such as a gene variation that makes it likely we will get cancer). However, whether a mutation or gene variation is beneficial or deleterious really depends on the situation. In some contexts it may be good to have a protein that burns energy faster, because you can use that energy to run faster; but in other contexts it can be bad because you will need to eat more food to maintain your energy levels, and there may not be more food to eat. Therefore, in order to get a 'good' gene you have to be in the right place at the time and with the right mutation. Good or bad is simply context-dependent! I think this brings a whole new meaning to the age-old expression, 'timing is everything!'
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