Blog Post Module 4

 Mutation is a major source of variation that natural selection can act upon to create evolutionary change. Mutations can have positive or negative impacts on the population or organisms themselves. This is connected to Darwin's idea that individuals in a population vary in their traits. I think mutation rates do evolve. Genetic changes from one generation to the next could cause increased mutation. Mutations can cause deleterious alleles to accumulate but it also has the possibility to allow beneficial alleles to be acquired. During cell division, DNA has to be copied. With so much DNA there is an increased risk of typos or mistakes being made in the new copy. This can lead to mutations. Additionally, mutations can be passed from parent to offspring. When someone inherits one abnormal copy of a gene, it makes it all the easier for mutations to build up. This is what happens sometimes in the case of cancer. Mutations in cells accumulate to cause cancerous growths (a.k.a. tumors). Size of the genome can also impact rate of mutation. Larger genomes have a higher likelihood of gaining errors. Multicellular organisms also display higher mutation rates. This makes sense because when our cells divide it doesn't mean there is a new generation of us, whereas when unicellular creatures divide it always represents a new generation. One multicellular organism could accrue many mutations before passing them on to offspring compounding the process. If we all arose from a common ancestor as Darwin believed, then at one point we all had the same rate of mutation. However, that mutation is also part of the reason why life diverged into its many forms that now have many different rates of genetic change and mutation. Certain organisms have biological and chemical predispositions that make them more or less likely to undergo mutation as well.

It is generally seen that higher mutation leads to greater genetic diversity and accelerated evolutionary adaptation. However, high mutation rates can also limit this same thing. It all depends on maintaining a balance between positive and negative mutational impacts on a population's fitness. For instance, a study by Kathleen Sprouffske studied mutation rate in E. coli. They found that E. coli with the highest mutation rate showed reduced adaption and difficulty thriving in different environments. There mutations made them successful only in very very rare instances and environments. On the other hand, modest rates of mutation actually showed the greatest rates of evolutionary adaptation and survival. So too much of something is not always better. As with energetics and many other biological processes, it is all about finding that sweet spot. And typically that is somewhere in the middle.

Low mutation rates can be adaptive in many circumstances. Although there isn't as high of a chance for quick evolutionary change, the genome is conserved to a greater degree in this case. Less mutation means less chance for deleterious alleles to negatively impact a species. Low mutation could be beneficial in circumstances where organisms are well suited to thrive in their specific environment. If high rates of mutation were to occur in that case, these creatures might become ill-suited to survive and actually die. Where they were once very successful based on previous evolutionary change, they could be killed off in a fairly short period of time. Sometimes specificity can be the downfall. A small change can lead to a big issue.

Source: https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007324, Title: High mutation rates limit evolutionary adaptation in Escherichia coli., Authors: Kathleen Sprouffske, Jose Aguilar-Rodriguez