Genetic Drift and Natural SelectionBy Ryan JahansoozAssisted by Tyler Voss, Zac Foster, and Hunter Wolfbear DrobenaireCompleted 11/6/13 in Bio Lab 001 Section 16Abstract:Natural selection and genetic drift are the two major deciders of the future of a species. Genetic drift is left up to chance and involves random mating as well as unforeseen chance- incidents like natural disasters. Natural selection is a more concrete method in which definite genetic mutations give the holder a specific advantage over others of its species that either allows it to breed more, or live longer. Experiments testing the effects of natural selection and genetic drift involve using computer programs that can quickly come up with the most likely results of any given set of genes in a species. These simulations allow us to easily test the outcomes of a species without having to wait for several generations. The program used did indeed make this experiment quite simple in that we were able to acquire a plethora of information on genetic drift and natural selection in only a few minutes.Introduction:The most crucial aspect of understanding genetic drift lies in understanding how genes work. Genes in an organism can either be heterozygous or homozygous, meaning that you can either have two of the same gene, or two different ones. Genes can also be dominant or recessive. If an organism is heterozygous with one dominant and one recessive, the dominant one will take priority. The only way for an organism to show signs of having a recessive gene is to be homozygous with that gene. When a child has blonde hair when its parents are both brunette, it means that both parents are heterozygous with one dominant gene for brown hair, and one recessive gene for blonde hair. Of course, there is only a 25% chance of the child not having a gene for brown hair.Genetic drift utilizes the way that genes work (being recessive/dominant or homozygous/heterozygous) to spread out the genetics of a species and create new combinations out of new mutations. If a group has 70% of one dominant allele and 30% of one recessive allele, you can predict the genetic frequency of the next generation. This also allows for a random element to be introduced that could potentially shift the balance of genes to one side or the other. In a small population, the number of organisms with the dominant allele couldspike up due to how common it is and how easy it is to spread, but the recessive gene could alsocome out on top, with a bit of luck. This essentially creates different, isolated populations purelyby chance.Natural selection, on the other hand, plays a much more solid role in choosing which organisms pass on their genes to the next generation. The genes that an individual has will give it specific traits that are not shared with others in its species. These random traits can either give the organism an advantage over its rivals, or cripple it. An example would be a pack of wolfs hunting in the winter. One wolf might be faster and stronger, and thus is able to huntmore efficiently, live longer, and produce more offspring. Another wolf might have a unique scent that makes it extremely appealing to the opposite sex, which also allows it to breed more even if it doesn’t live as long. The last wolf was unfortunately born with short legs, dull teeth, and a small brain. Unable to hunt or find a mate, this wolf will likely die before passing on its genes. This process of natural selection results in two progressive genes growing more prominent in the gene pool, while helping push out the undesirable ones.In the lab, we used a computer simulation to model the new generations of a populationand what their genotypes will be. We thought that it would be more likely that smaller populations would change a lot, while larger populations would change less overall. This was attributed to the fact that in larger populations, there are more opportunities for genes to be passed on or mixed together. Methods and Materials:The lab was set up in a way that did not allow for error, but there was an error with collecting data for the standard deviation of a population of 1000. The experimental procedures for this lab were adapted from a previously supplied protocol. Results:The simulation program that was used to model the populations over time allowed us toeasily acquire the data required to test our hypothesis. In Fig 1, you can see the differences caused by changing the initial population of a group. As the generations go by, the smaller populations experience an increase in standard deviation from the original allele, while larger populations deviate less. To get a clear picture of the differences between populations, look at Fig 2 and Fig 3.Fig 1: Change in Mean and Standard Deviation of Frequency of Allele A in Populations of Different Size Over TimePoP Generation0 25 50 75 100 125Ave SD Ave SD Ave SD Ave SD Ave SD Ave SD1000 .5 0 .505 .055 .498 .079 .494 .901 .49 .049 .496 g500 .5 0 .49 .082 .481 .117 .492 .127 .487 .199 .486 .17250 .5 0 .479 .12 .471 .167 .453 .21 .448 .24 .456 .261100 .5 0 .497 .183 .533 .241 .536 .283 .519 .327 .506 .35650 .5 0 .529 .209 .562 .282 .572 .328 .584 .36 .611 .39225 .5 0 .479 .326 .526 .376 .531 .424 .532 .458 .538 .48Fig 2: Average Frequency of Allele “A” in Populations1000 500 250 100 50 2500.10.20.30.40.50.60.70255075100125Fig 3: Standard Deviation of Allele “A” in Populations1000 500 250 100 50 2500.10.20.30.40.50.60.70.80.910255075100125To test the effects of natural selection on different populations, we used a similar program. The model that we got from this simulation suggests that in real populations of organisms, natural selection will reduce the frequency of popular alleles while increasing the observable frequency of dominant alleles. This can be seen by looking at Fig 4, which has an included control group as well as four randomly selected values to show the consistency of the data. The number after the “=” sign signifies the chance that that allele will be passed on.Fig 4: Mean and Standard Deviation of Allele “A” Frequency for 100 Populations with DifferentSelective PressuresAllele Fitnesses Allele “A” Frequency Mean Allele “A” Frequency StandardDeviationAA=1; Aa=aA=1; aa=1 (control group)1 1AA=1; Aa=aA=1; aa=.98 1 .97AA=1; Aa=aA=1; aa=.95 1 .94AA=.95; Aa=aA=1; aa=.95 .94 .94AA=.9; Aa=aA=.9; aa=.9 .9 .9AA=.8; Aa=aA=.6; aa=.7 .79 .71AA=.7; Aa=aA=.6; aa=.8 .71 .79AA=.6; Aa=aA=.8;