DNA Mutation: The Ultimate Elixir of Life

Germ-Line DNA Mutation: Evolution and Genetic Disease

Let’s move on to the “good” mutations commonly associated with sexual reproduction, the method by which humans (and most complex life) reproduce.

In short, sexual reproduction is the combination of half of one organism’s DNA with half from another (sperm and egg), both of which have  at least some mutations due to micro failures in repair systems mentioned above. The combination of the two different halves results in various mutations within the egg cell.

Generational Mutations: Not Localized

The most important point to understand about this type of reproduction is its effects on the child. Since each child of any organism begins development as one cell, any mutations in this cell will affect every cell in the final product. For example, a DNA mutation for dark skin in the fertilized egg cell makes the whole child dark skinned. A mutation for dark skin in a cell later on in development will only affect that cell’s descendants, making a birthmark.

Sexual Reproductions: Benefits Outweigh the Costs

If you think about it, sexual reproduction doesn’t make a lot of sense. Why would life give up the ability to replicate like crazy and replace it with a more energy intensive form of reproduction? Not only is finding a mate time consuming and difficult, but only half of the DNA from each parent continues on. In contrast, a bacteria can be “sure” all of its DNA survives into the next generation since it literally becomes two copies of itself. The explanation is that all of the risks associated with sexual reproduction are outweighed by the opportunity for beneficial genetic mutations. As you can see, evolution favors life forms that can evolve faster than others.

Why did sexual reproduction evolve? It makes children different from their parents so that they can (hopefully) be better suited for life on Earth. The mechanics of this process are complex and will be covered under specific genetics posts. Obviously this is a double edged sword; mutations in children can be bad as well. These children will die out, making room for the “good” mutants, allowing evolution to occur.

Sickle Cell: A Classic Example of Human Evolution

Evolution in this way has produced various different adaptations in humans. The most well known human evolutionary story is that of sickle cell anemia. This condition is most common in people from a certain region of Africa. Most developed nations see sickle cell as a genetic disease. However, by studying its evolution, a fascinating story comes to light.

Sickle cell anemia is a disease caused by the change of one letter in the hemoglobin protein’s DNA code. This change makes all the hemoglobin in a red blood cell come together in long strands, changing the shape of the cell and making it difficult for blood to travel through the  body. Thus, scientists wondered why so many people in Africa have this DNA mutation if it is so bad.

After studying this phenomenon, it was observed that red blood cells with sickle cell are resistant to blood parasites. Specifically, sickle cell makes it difficult for malaria to spread through one’s body. After this connection was made, scientists looked at prevalence of malaria in places with sickle cell patients. Sure enough, sickle cell patients were most concentrated in places where malaria was a problem. This indicated that the sickle cell mutation provided a large survival advantage to people in these areas and slowly came to dominate these population. The advantage simply outweighed the downsides.

Conclusion

Throughout the history of Earth, there have always been opposing forces working on life forms. While the universe tries to break down everything into its most stable form, evolution is working to make organisms resistant to these forces. However, there is an interesting paradox present in this relationship. While mutations are the biggest threat life has to defend against, evolution too draws on these mutations to empower life. In short, evolution uses the laws of nature to fight against the laws of nature.

In our lives, we are defined by the countless small decisions we make, compounded over long spans of time. Of these decisions, most will not provide the result one desires. After all, the universe only guarantees chaos and disorganization. With this understanding, we invest time and energy to activities, knowing that success is something that is not granted without effort and must be fought for. Similarly, evolution progresses by experimenting with random changes until one is discovered which works. Just like our lives, these successful and failed “decisions” define the world we live in. It is truly amazing that life can rebel against the universe in such a way, turning the problem into the solution.