Genetics has fascinated man since the discovery of DNA. The mapping of the human genome has only further enhanced this fascination by shedding light on whole new areas of study. Not only do genes reveal the secret of the past, it tells us a lot about what is happening now and even gives us an idea of what we can do in the future.
Our genes make up who we are physically and mentally. But this influence is not a one-way street. Not only do our genes make us who we are, but we also have an influence over our genes. It’s an interesting relationship and one that you should know about.
In this book summary readers will discover:
- Genes and the information we gain from them
- What genes tell us about sex
- Genes, diet and behaviour – How are they linked?
- How athletes are genetically different
- What can alter genes?
Key lesson one: Genes and the information we gain from them
We all know that our genes dictate what we look like. Our natural hair, skin colour, eye colour, even the length of our fingers are determined by genes. Interestingly, on closer inspection, the way we look could also give us interesting clues about our genes.
Take for instance the human eye. It is often said that it is the window to the soul but maybe it would be better to think of it as a window of information for many genetic conditions. Obviously, you would still have to get tested to confirm, but the eyes offer a clue.
If a person’s eyes are particularly close together, for example, there is a chance that they could have Fanconi anaemia. Or the tell-tale sign of Down syndrome whereby the outer corner of the eye is higher than the inner corner of the eye. Heterochromia is another example of the effect genes can have on our eyes. This results in one eye having a different colour from the other. Another effect genes can have on eye colour is an uneven distribution of pigments.
But once again, this is a two-way street. Having information about someone’s genes can also tell you a lot about how they look. It is what is used in forensics and can help us imagine what people looked like in the past. A classic example of this was Ötzi, the Stone Age man whose mummy was found in 1991. Over five thousand years old, scientists were able to extract DNA from the mummy’s hip to gain more insight. With this, they were able to determine that Ötzi was likely light-skinned with brown eyes. Scientists were also able to show that he had Type O blood and was lactose intolerant.
While genes may be able to provide detailed information about people, it is not as effective at determining how genes will be passed from parent to offspring. This for the most part is because that there are passive genes that are passed from generation to generation and who they will affect cannot be determined accurately. What affects the parent may not affect a child and vice versa.
This was apparent when a seemingly prime Danish sperm donor, Ralph, fathered over 40 kids around the world. He carried the passive gene for neurofibromatosis, a genetic disorder. Unfortunately, many of the children he fathered ended up with neurofibromatosis even though he was a healthy, genetically sound donor. The way in which a gene is expressed cannot be determined because variable genetic expressivity often occurs. In fact, even between identical twins differences can occur due to the expression of the genes. Identical twins suffering from neurofibromatosis for example displayed vast differences in the way the disorder was expressed. One twin had a badly disfigured face whilst the other had no physical traits and instead the disease manifested in the form of seizures and memory loss.
Variable genetic expressivity proves that even if we start out with the same DNA, how a gene is expressed can be totally different.
Key lesson two: What genes tell us about sex
Basic biology taught us that humans have 23 pairs of chromosomes. Of these, one pair codes for sex. If you are male, you have an X and Y chromosome and if you are female you have two X chromosomes. The Y chromosome carries the SRY gene which is responsible for the hormones responsible for increased body hair and development of the male sex organs.
However, as the study of genetics continues, it was discovered that more than two sexes are a possibility. There are many genetic variables present which code for different aspects of our sex. This goes from everything from the shape of sexual organs to the sound of our voices. With all these variables present, it is also possible for a person to be both male and female. An example came from Ethan, who for all intents and purposes, is a young boy. However, genetically, Ethan was born with two X chromosomes. How was this possible? Well, even though Ethan lacked the SRY gene found on the Y chromosome, he had SOX genes that are also responsible for sex determination. During development, one of Ethan’s SOX genes were activated twice that caused it to mimic the SRY gene.
So, even though the majority still fit into the traditional XX and XY sex determination, there are still individuals who exhibit the complexities of genetic expression. These expressions might actually go unnoticed and therefore further research is needed to see just how many variables truly exist.
Key lesson three: Genes, diet and behaviour – How are they linked?
Did you know that genes determine how our bodies react to certain foods? As incredulous as it may seem, genes can determine your diet and likewise, if you have a genetic condition certain foods can help you.
We are familiar with how sailors in the Middle Ages suffered from scurvy. Once it was determined that lack of Vitamin C was the culprit, many ships ensured that they had enough citrus fruits onboard that could prevent the sailors from getting sick. Whilst everyone needed the vitamin C to stay scurvy free, a few sailors had a genetic advantage. They possessed a variation of the gene SLC23A1, which enabled them to metabolize vitamin C efficiently meaning they needed to eat less citrus as compared to other sailors.
The way our bodies metabolize caffeine is also determined by genetics. If you have a single copy of a gene called CYP1A2, you metabolize caffeine slowly and a small cup of coffee can give you the boost you need during the day. However, if you possess two copies of the gene, you metabolize caffeine faster and even a big cup might not do the trick. Interestingly enough, the CYP1A2 gene also has an interaction with nicotine. If you are a smoker, this gene gets activated making your morning cup of coffee less effective.
But beyond these genes, genetic disorders also exist which may influence a person’s diet greatly. People with hereditary fructose intolerance, for example, cannot metabolize fruit and those with ornithine transcarbamylase deficiency can’t eat high protein foods. So, don’t be too quick to judge those with strange diets, their genes might be dictating what they can and cannot eat.
Key lesson four: How athletes are genetically different
When it comes to athletes, it’s quite obvious that some of them are genetically blessed. Basketball players are chosen because of their superior height and what about Michael Phelps and his enormous arm span? Genetic conditions could also end up being an advantage in some cases. Skier Eero Mäntyranta, for example, had primary familial and congenital polycythemia which results in higher than normal red blood cells. The more red blood cells you have, the more oxygen is circulated in the blood which gave her an advantage when skiing. Even pain endurance can be altered by genes. A mutation in gene SCN9A, for example, results in a person not feeling any pain at all since no signals are sent to the brain.
The way you train if you are an athlete can also change the behaviour of your genes and thus the effect they have on your body. An athlete who exercises vigorously have bones that grow in order to support the muscle mass they develop. If they didn’t, it would most likely lead to injury when they played their specific sport. To be fair, it’s the same thing that happens when you put on weight as well. Your genes instruct your body to adapt. Therefore, without proper exercise, your bones actually tend to deteriorate the same way astronaut’s do. Because it is not in use, your body thinks that it is no longer necessary to produce bone cells. The destruction of cells occurs more rapidly than cell replacement and weakens your bones overall.
Key lesson five: What can alter genes?
Yes, you are born with your genes, but that does not mean they cannot be altered later on. There are many factors, caused by your actions and your environment that can cause these alterations. Air travel can expose you to radiation that can damage your DNA, spending hours tanning in the sun and drinking copious amounts of alcohol also cause genetic mutations. These mutations can all lead to cancer. On the flip side, if you treat your genes right by following a healthy diet, there is also a possibility that you could protect yourself and your genes from harm.
External factors which are not in your control, however, are harder to avoid. Alterations to our genes due to these environmental influences are referred to as epigenetics. The events that alter your genes could even occur before you were born. Mothers who were pregnant during 9/11 had kids with an increased risk of anxiety. If you were bullied as a child, your SERT gene may be deactivated meaning that you have a dulled reaction to stressful situations as an adult.
This alteration of genes also means that it gets passed on to the next generation. How it will be expressed is unknown but, it will be present nonetheless.
The key takeaway from Inheritance is:
Our genes play an important role in our lives, controlling much more than we could ever expect. But, we must also be conscious of the fact that this is not a one-way interaction. We also have an influence on our genes. Our diets, environments and even the way we exercise can influence our genes which in turn will influence our bodies. Understanding how these interactions work can be extremely beneficial to your health and lifestyle.
How can I implement the lessons learned in Inheritance:
By learning about your genes, you could gain all the knowledge you need to adapt your lifestyle and diet to ensure that you live your best possible life. In addition, genetic testing can help identify any potential health threats that may occur in your future or that may be passed to your children.
