Mutations That Occur In Gametes

The first force of evolution is referred to as mutation and remains the only source of new genetic material or alleles. Mutation occurs during DNA replication, instead of the identical replication, an error occurs during the process. Basically, something is tweaked during replication that changes the bases of a gene. If the problem is not detected and corrected,a mutation results. As the book articulates, so much of DNA is non-coding that many mutations will not affect an individual's health or well-being, but a mutation in coding DNA will cause a different outcome, whether it be positive or negative. Mutations that occur in gametes are the ones that will change future generations. There are different types of mutations that are caused by numerous

events. The first one to discuss is a point mutation, or replacement of a single nitrogen base,; which in itself has two separate distinctions. The first one is referred to as a synonymous point mutation which produces an altered triplet in the DNA but the alteration does not affect the amino acid and the protein performs the same. In the case of a non-synonymous point mutation, the altered triplet results in a different amino acid entirely, which can cause some noteworthy changes. Another example is a frameshift mutation which occurs when an extra base is inserted, causing the reading frame to alter or stop entirely. This creates an non-functioning protein. The mutations that can invoke the most change is called a transposable element mutation. These genes will copy themselves on entirely different parts of the DNA sequence, causing irreparable changes.

The second mechanism of evolution is Darwin's theory of natural selection or organisms with environmentally advantageous characteristics will have higher survival rates and live to pass on those characteristics to their offspring.

Eventually, almost all the members of the species will posses the desired characteristics and this is how species evolve. For example, if a there was a species of frog with two distinct coloring patterns, light and dark let's say, if the darker coloring allowed better camouflage from predators, eventually the lighter frogs would be killed by predators and only the darker frogs would live to reproduce. There are several patterns of selection, one of them being directional selection. Directional selection favors one extreme form of a trait over another; the example mentioned in the book is human brain size. Human evolution has clearly favored larger brains. The next pattern is stabilizing selection, or favoring the average version of a trait. Again with human evolution, human babies that are an average weight have a better chance of surviving and reproducing then the lightest and heaviest ones. Disruptive selection refers to a discontinuous variation pattern or reproduction occurs mostly at the extremes of a

population

The third driver of evolution is genetic drift, which is defined as a random change in allele frequency over time. In humans, genetic drift occurs over a long period of time, rather then at a single point. The chances of an allele's frequency changing rapidly increases with population decrease; they are inversely related. In an endogamous society, for example, genetic drift may occur more rapidly because reproducing outside the group is highly discouraged. The founder affect refers to a specific type of genetic drift when a small group of a large parent population migrates to a new region and is reproductively isolated. As the founding population reproduces the gene pool diverges even farther from the original parent population. For instance, the Native Americans descended from the ones that migrated from East Asia to North America have an unusually high frequency of type O blood, while eastern Asia has a much lower occurrence of type O blood.

The final factor of evolution is called gene flow otherwise known as the transfer of genes across population boundaries. In simplest terms, members of two different populations create offspring. The key factor for determining the amount of gene flow is proximity to potential mates; the less actual distance between populations the greater chance of gene flow. Gene flow decreases genetic variation of two populations over time and is highly influenced by social factors, like if a society is endogamous or exogamous. There are specific genetic tags that give evidence of gene flow across large regions, such as the ABO blood group system that shows how certain populations migrated from east to west.

Sickle cell anemia is a disease caused by abnormal hemoglobin and produces sickle-shaped red blood cells. At first glance, sickle cell anemia seems like a trait that should not have survived this long, especially since before modern medicine, the mortality rate was 80% before reproductive age. However, in the mid-twentieth century scientists began noticing a relationship between the number of people with sickle cell anemia and high malaria concentration areas. Anthony Allison reasoned that individuals with sickle cell were less likely to contract the deadly malaria disease because the cells themselves were poor hosts for the parasite. . This connection makes sickle cell a perfect example of balanced polymorphism; the two alleles that code for this disease would not have survived this long if they did not decrease the chances of contracting malaria.

As aforementioned, there is a difference between a point mutation and a frameshift mutation. A frameshit mutation is far more likely to create a defective protein because the insertion of a base throws off the entire gene reading mechanism. Everything shifts over one, so an entirely different protein is coded than the one originally intended. A point mutation is the replacement of a single nitrogen base, so there is a much higher chance that the replacement base still codes for the same amino acid, meaning the protein could still function normally.

The founder's effect, as previously mentioned, occurs when a small portion of a large parent population migrates to a reproductively isolated location. Because the new group is far removed from other populations and can only create offspring among themselves, divergence from the parent population can occur rather quickly. This is illustrated in the example of the Native Americans who migrated from East Asia to North America. Because the original migrating group had a high frequency of type O blood, that trait was passed down through the generations. Still today a high number of those Native Americans have type O blood, but the parent population they left in East Asia does not.