Force Becky Gonzalez Genetics 2450 Lab Section 1262 March 2, 2011 Genetic Drift as an Evolutionary Force Genetic drift, along with natural selection, mutation, and gene flow, is one of the basic evolutionary forces of evolution. Evolution is the method by which allele frequencies in a population change over time. This process can be random, where the changes occur through genetic drift (Hahn and Bentley 2003).
Genetic drift causes these random changes in allele frequencies, which result from random fluctuations across generations.
Genetic drift happens in ALL populations, large and small, but affects them to a different degree based on size. Smaller populations tend to be significantly affected by genetic drift, while populations of a much larger size might experience some resistance. Although genetic drift usually occurs with one or more of the other evolutionary forces, genetic drift itself can cause extreme changes in allele and genotype frequencies. By chance alone, it can cause the elimination of a particular allele.
Population genetics uses genetic drift, natural selection, mutation, and migration as tools to understand how and why populations undergo changes in allele and genotype frequencies, as well as its effects for future generations. To recognize the effects of genetic drift on a population, an understanding of the Hardy-Weinberg Equilibrium must be met. This theory states that if certain conditions are met there will be no evolution occurring in a population.
The Term Paper on Population Change In Scotland
What can be said about population change in local government areas in Scotland and the change in age structure for 2000-2010. In the first part of this assessment I will describe the information provided on the chrorpleth map and a graph by the General Register Office of Scotland to help define the change in population in Scotland also the change in the age structure in Scotland between the years ...
Simply put, if a population is in HWE, then that population is not evolving, and you can expect the population to stay frozen from one generation to the next in terms of allele and genotype frequencies. Conditions to be met include: 1. ) the population must be infinitely large, 2. ) no natural selection occurring, 3. ) no mutation occurring, 4. ) no migration (gene flow) occurring, and 5. ) random mating must occur. However, if even one of these conditions is not met, deviations from the initial genotype and allele frequencies will occur and evolution will take place.
Using this theory as a basis will help distinguish the effects of the four evolutionary forces, specifically genetic drift, in a population. Genetic drift occurs from sampling error; however there are different ways sampling error comes about in a population. First, as stated earlier, genetic drift can occur when population size is small. When genetic drift occurs in a small population there is a higher chance of allele frequency to increase or decrease over time drifting toward one extreme or the other at a faster rate.
Eventually the alleles may come to frequencies of 1. 0 or 0. 0, where at this point fixation has occurred. One allele has been lost in the population (0. 0) and no further changes in allele frequency can be seen. As this occurs, heterozygosity decreases as well due to the increase in frequency of one allele and decrease of another. Ultimately genetic drift causes the population to lose variation. The probability of fixation due to genetic drift is equal to the frequency of alleles in that population. Another form of sampling error is through a founder effect.
This occurs when a population is made up of a small number of individuals that in time may grow to a larger population. This population, however, will consist of genes present from the original “founding” population. A third form of sampling error that causes genetic drift is the bottleneck effect. Bottleneck effect happens when population suffers a great reduction in size. When such events occur, the small population is then vulnerable to genetic drift acting upon it. Natural disasters such as earthquakes, floods, or fires may reduce the size of a population drastically and kill victims unselectively.
The Essay on Genetic Disorders 3
Each year a number of children are born with biological defects that impair normal function. For THREE of the following conditions, discuss such aspects as the biological cause, the methods of treatment and possible means of detection and/or prevention. One lethal disorder inherited as a recessive allele is Tay-Sachs disease. This is caused by a dysfunctional enzyme that fails to break down brain ...
The resulting small surviving population is unlikely to be representative of the original population in its genetic makeup. The gene pool of any surviving populations may have been, by chance, different from that of the original population before catastrophe struck. (Campbell 1990).
Genetic drift also causes genetic divergence among populations. Allele frequencies in separate populations change within themselves, separately from other populations, causing differences between populations.
It is also noted that isolated or secluded populations may diverge from one another as a result of genetic drift. The amount of divergence that occurs between the populations in based on the extent to which mutation and migration act upon (Song et al. 2006).
Two evolutionary forces, migration and mutation, can balance the effects of genetic drift by introducing new or different alleles into a population from different organisms coming into or occurring in the population. Gene flow occurs when organisms migrate in or out of a population and contribute their genes to a recipient population.
This spread of alleles result in changes in allele frequency in the original population as well as the recipient population. Mutation introduces new variations into a population and causes a change in allele frequency. Mutation is the ultimate source of new genetic variation in a population. From mutation, other evolutionary forces can act upon the changes in allele frequencies causing evolution to occur. However, mutations occur at an extremely low rate and the extent of its effect on allele frequencies in a population is largely determined by the other evolutionary forces.
Genetic drift, mutation, migration, and natural selection are capable of changing allele frequencies in a population over time, but natural selection is the only evolutionary force that can cause an organism or population to adapt. Natural selection is the process by which traits evolve that increase the organism’s fitness (Russell 2002).
The Essay on Genetic Engineering 17
The selective Engineering of Genetics is invaluable to the health and happiness of humans. The importance of this issue has played second fiddle to the arguments, for and against genetic engineering. This essay will discuss the impact of genetic engineering on everyday life, for example genetic disorders, disease and how its impact on life in the world today. Although the opinions differ greatly, ...
Natural selection then causes genes of the “fittest” organisms to be passed on to their children and continue to be in the population as long as those genes will allow for the most reproductive output.
As the environment changes or if a disastrous event such as in a bottleneck effect, natural selection change allele frequencies by selecting those alleles that best withstand the changes that occurred. With a small population size, random genetic drift is more effective than natural selection in determining the fate of new alleles. Eventually fixation can occur, reducing the reproductive capacity of a population, to the point of possible extinction (Whitlock 2000).
The evolutionary forces acting on a population, especially genetic drift, are very important when studying population genetics.
Since Sewall Wright first introduced the idea of genetic drift in the 1930s, we have been able to extend this knowledge into other evolutionary forces acting on a population. Using this knowledge of genetic drift, we are able to understand how and why some species go extinct, the lack of genetic variation within populations, and the increase of genetic divergence between populations. Literature Cited: Campbell, N. A. , 1990 Biology, 2nd Edition. Benjamin/Cummings Publishing Company Inc. , p. 443 Hahn, M. W. , and Bentley, R. A. , 2003 Drift as a mechanism for cultural change: an example from baby names.
Proceedings: Biological Sciences Vol. 270: S120- S123 Russell, P. J. , 2002 Genetics, 3rd Edition. Benjamin/Cummings Publishing Company, Inc. , CA. p. 631-632 Song, S. , Dey, D. K. , and Holsinger, K. E. , 2006 Differentiation among populations with migration, mutation, and drift: implications for genetic inference. Evolution Vol. 60, No. 1: 1-12 Whilock, M. C. , 2000 Fixation of new alleles and the extinction of small populations: drift load, beneficial alleles, and sexual selection. Evolution Vol. 54, No. 6: 1855-1861
