Major Evolutionary Issues - Assignment Example

?Evolutionary Question Genetic drift, like natural selection and genetic mutation, is one of the mechanisms by which evolution can occur in a select population. Genetic drift is also referred to as the Sewall Wright effect. It is when the allelic frequencies are changed in a random population due to chance. This could effect a population in terms of a natural disaster or a change in predator-prey styles, which would lead to a statistical change in the way in which allelic combinations are calculated. At the genetic level, it is important to address the genetic components of the driving force in genetic drift. When meiosis occurs, genes are segregated at random and events such as crossing over can occur, which causes increased genetic variation. In larger populations, the allelic combinations typically stay stable over time. However, in smaller populations, any type of variation or production of one gene over another due to chance can have a large change in the gene pool frequencies. The most useful way to think about this concept is in terms of the Hardy Weinberg Equation, which is a quadratic formula that calculates the genetic frequencies of the homozygous dominant, homozygous recessive, and heterozygous expressions. The Hardy Weinberg Equation uses the letters P and Q in order to addresses the alleles for a population with homozygous dominant being p2, homozygous recessive being q2, and heterozygous being pq. Normally, in a standard population and statistically valid population, the ratios would be the same. Like stated above there are multiple factors, which can then affect the ratio of these allelic frequencies. Some of the organisms may survive due to supremacy of the traits they expressed or the randomness of gamete formation may lead to an unproportional expression in traits. For example, lets consider a population which has allelic frequencies of p=0.3 and q=0.7. The ratios expressed by the Hardy Weinberg Equation would then be (0.3)2, 2(0.3)(0.7) and (0.7)2. As the proportion of genes expressed changes, so does the Hardy Weinberg Equation; one of the allelic frequencies will increase while the other decreases. The ratios expressed would then be: (0.2)2, 2(0.2)(0.8), and (0.8)2. The effects of genetic drift in smaller populations are much larger than those experienced in larger populations. This is because a statistical change in allelic frequencies in a smaller population due to chance has a larger and more significant effect because the population, N, is smaller. Therefore, the effect size is larger. The reason that it is not as powerful in populations with a large N value is because it is thought that the chance of one allelic combination being produced over the other is negligible, therefore they cancel out which shows that there is no real resulting chance in the frequencies of the gene pool. DNA replication is a process, which is ongoing at every moment in every organism. It is important in order to ensure that the structure of the genetic code remains viable for reproduction, however the code becomes more disrupted every time that it is replicated. These mistakes are mutations, which occur in the replication of DNA can cause either desirable or undesirable traits to form. This is one of the basis in which evolution is thought to occur. Different types of mutations have different effects on evolution. Replacement mutations are much lower than substitution mutations. These are thought to effect neutral genes, which remain structurally similar over time. Substitution mutations are thought to happen in genes that are dynamic and are quick changing in that this is the main mutation, which promotes the most genetic variation. Conservation biology is the field of biology that is directed specifically at understanding and protecting the biodiversity of the Earth. Understanding the role and relationship of species in their habitats and ecosystems does this. Specifically, Templeton was concerned with the human activity, which was having an affect on genetic variation of the collared lizards in the Missouri Ozarks (Crotaphytus collaris). Humans have made huge impacts on the environment of the Earth, which has drastically changed not only the face of the landscape, but also has effects on the ecosystems in these locations. Many times, humans will move into these areas in an attempt to harvest the areas natural resources and will process them in order to form products for society. An inherent danger and consequence of tampering with the ecology of an area is that it will affect many parts of the biodiversity. By removing parts of the ecosystem, whether it be flora or fauna, it effects the other relationships with organisms that live in the area. This then can move to affect whether certain organisms will continue to flourish and those that will die out. In this way, artificial selection is a method for evolution, which can either prove good or bad. Plotting the course of evolution is also an extremely important part of conservation biology due to the goal of this field is to promote the continuation of species, especially those that are at risk or are currently going instinct. As stated earlier, the tampering of an ecosystem can cause artificial selection. The disruption and alteration of a habitat can facilitate a change in the balance of allelic combinations. In addition, it can also drive evolution and expansion of an organism’s area through founder effects. Lastly, understandings of the mechanics of changes that occur inherently in a habitat are important to conservation biologists. Even the slightest disruptions in the delicate balances of nature can have drastic consequences and effects on the local inhabitants. This can be due to either the harvesting of resources to the dumping of wastes in an environment. This can also drive evolution by killing out species that cannot adapt to these changes that occur. All biological and human factors have to be considered when looking at a species evolution and future in conservation biology by trying to account for all variables of change. Migration is the movement of genes within a population. This can be taken in a eugenics principle in order to increase the breeding potential of the decreasing chick population. Selection of desired traits can be used in order to increase the frequencies of the desired set of alleles. As a result, the effect of the migration and selection will amplify the desired traits within the population. Due to the declining population, genetic drift can also be used to account for a larger increase in the population. Genetic drift has the highest effect on populations with a smaller N value. As a result, the genes, which promote greater survival and reproduction, will increase in an unproportional amount compared to the unfavorable genes. Thus, the effect on the population will be much larger resulting the more favorable genes being passed on at a higher frequency. Inbreeding will have a deleterious effect on the population. It is known that when organisms mate with those that are genetically similar that many genetic abnormalities will result. Since the populations of chickens are often isolated and small, there is a large proportion of inbreeding. This inbreeding decreases the genetic variation in a population, which due to the small population size, means that this has an even larger effect on the population, which increases the negative effects in the population. All of these effects need to be taken into consideration because they are not mutually exclusive of one another. This is due to the fact that as driving forces of evolution, they all affect each other. There are a couple different ways in which evolution can result in new populations of species resulting from a single, original species. This is known looking at the course of the evolution of all creatures, specifically starting with the single cell organisms, which then developed into the multicellular and more complex organisms that exist today. This is achieved through adaptive radiation. Convergent evolution is when a species or two become more diverse and different genetically. This is seen in many different species such as the many different types of monkeys, dogs, etc. This can be achieved through migration, geographic isolation, etc. If the species were able to come back into contact with each other, there are two different scenarios, which could occur based on a few factors. If there were too much genetic variation that has occurred among the population, they would not be compatible. However, if there were not a significant amount of genetic variation, then the species would be able to remerge together through convergent evolution. This could lead to either a reintegration of the species or the creation of a new hybrid species. The Wallace Effect is hypothesized by Alfred Wallace, which deals with natural selection on the basis of reproductive isolation. He combined the notions of divergent evolution in that if the species were to become reintroduced to one another, it would result in a hybridization of the two species. What he hypothesized is that the hybrids that would be formed would be less adapted to conditions than the two species that were together separately. As a result, nature would select them to be less fit and they would not survive. Thus, nature is able to form its own barriers to keep organisms more fit by creating reproductive isolation. Koopman was able to test this construct by using drosophila flies (a model organism) in order to see if this was true. For the experiment, he chose D. pseudoobscura and D. persimilis. In each generation, he allowed the different flies to reproduce with one another. He then destroyed the succession hybrids that were created. He noticed that as he continued to do this, the drosophila started to only mate with members of their specific species. Thus the data began to show that the percentage of hybrids produced continued to get smaller and smaller. Thus he was able to prove Wallace’s hypothesis by keeping it under controlled conditions. An example of this is when horses and donkeys reproduce. Their offspring is infertile, thus they will be unable to survive and procreate. This is nature’s way of protecting the integrity of each species gene pools by creating a natural reproductive barrier. In the case of divergent evolution, the short time would have allowed for their respective gene pools to change as far as allelic combinations. In the case of minor divergence, the Wallace Effect would probably not come into play as far as being a reproductive barrier for hybridization. Since they are originally from a starting population, they would be able to reintegrate. Once the gene pools were incorporated together, equilibrium would set back in as both populations began to regress back to the original population. Another thing to consider is the ancestry of the individual populations. In the case of a short divergent evolution with limited separate genetic changes, the specific animal comes into question. Therefore, it is difficult to say depending on what was the reason for the divergence in the evolution to begin with. The McDonald-Kreitman test was developed by John McDonald and Martin Kreitman in order to observe selection as a result of molecular genetics. It was meant to prove the neutral theory of molecular evolution. It attributes that random effect of genetic drift cause a majority of the evolutionary changes that we see in populations at the molecular level. This means that when scientists observe the genome of populations, the changes in genetic traits are “neutral” in that the changes in genetic coding are unimportant and do not play a role in determining the fitness of the organism. The view plays on a role that the genetic code is degenerate by looking at codons that might differ in the actual nucleotide structure, but still encode for the same amino acid. The McDonald-Kreitman test used this on Drosphila in order to test the neutral theory of molecular evolution. They compared the specific DNA differences between the different genomes of the populations. They looked specifically at the protein differences and observing them between a couple different species of drosophila. The test showed strong evidence that the neutral theory of molecular evolution had strong internal and external validity. An example would be looking at the evolution of the genomes within the human race. Scientists have recently been able to decode the human genome. In the study of human evolution, looking at the differences between our ancestors and first homo sapiens and comparing it to the current human genome can help show how we have developed as well as provide reasons as to how it might be genetic drift and environmental factors which have shaped our development much more than just through genetic mutation. Codon bias is the probability that a certain nucleotide is going to be used over another to code for a specific amino acid (For Glycine GGT vs. GGG). This also shows why the genetic code is degenerate. There are multiple combinations of codon sequences, which code for the same amino acid. Therefore, one of the main questions to geneticist and scientists is why are some specific sequences chosen more often other sequences. This reflects the mutations and natural selection methods, which are the drive for evolution. The reason that specific codes are chosen over others is due to efficiency in that they are easier and faster to translate. Thus this advantage is one nature wants to select for advancement. This is stronger in more expressed genes and has been observed in both humans and drosophila. Read More