Table of content Introduction Effects of genetic drift Change in allele frequency Loss of genetic variation Loss of allelic diversity Founder effects Founder effect (i) genetic bottleneck Case study: Greater Prairies Chickens Founder effect (ii) Fitness effect of genetic drift Effective population size Genetic drift and natural selection Correlation between fitness and genetic diversity Conclusion References Genetic drift in natural populations Introduction If you flip a coin 500 times, a result of 300 heads and 200 tails might make you suspicious about that coin. But you would not be surprised if you flip a coin to 10 times, and an outcome of 8 heads and 2 tails shows. The smaller the number of coin flips, the more likely it is that chance alone will cause a deviation from the predicted result (Campbell & Reece 2008). In this case, the prediction is an equal number of heads and tails. Allele frequencies fluctuate unpredictably as a result of chance events, from one generation to the next mostly in small populations. Genetic drift is an overall change of allele distribution especially in a small population due to a random variation in the allele frequencies of an individual. Genetic drift (also known as random drift) occurs mostly in small population caused by severe reduction in population size called bottlenecks and founder events where a new population starts from a small number of individuals. Genetic drift is an example of a stochastic process where the actual outcome cannot be predicted because it is affected by random chance (Allendorf & Luikart 2007). The population genetic theory predicts that when populations are finite and random genetic drift takes place, increase in popul... ... middle of paper ... ... of Genic Heterozygosity in Natural Populations. II. Amount of Variation and Degree of Heterozygosity in Natural Ppopulations of Drosophila pseudoobscura. Genetics 54:595-609. Luikart, G., J.M. Cornuet. 1998. Empirical Evaluation of a Test for Identifying Recently Bottlenecked Populations from Allele Frequency Data. Conservation Biology 12:228-237. Méndez, M., J.L. Tella & J.A. Godoy. 2011. Restricted gene flow and genetic drift in recently fragmented population of an endangered steppe bird. Journal of Biological Conservation 144:2615-2622. Reed, D.H., & R. Frankham. 2003. Correlation between fitness and genetic diversity. Journal of Conservation Biology 17:230-237. Robert C.L., 1987. Loss of genetic diversity from managed population: Interacting effects of drift, mutation, immigration, selection, and population subdivision. Conservation Biology 2:143-158.
One of the phenotypes was poorly adapted for capturing wildloops. What is a possible explanation for why the nonadaptive alleles for this phenotype do not get removed from the population entirely over the course of many generations?
Stangel, P. W., Lennartz, M. R., and Smith, M. H. 1992. Genetic variation and population structure of Red-cockaded Woodpeckers. Conservation Biology. 6(2):283-292.
Test 4: All three phenotypic frequencies saw a reduction in their number as the homozygote fishes saw a reduction in their number and were not able to pass on their alleles to create either their colored fish or a heterozygote. Both yellow and blue allele frequencies decreased by the same
Species fragmentation could create long-term issues in the Cross River gorillas future. In a study, researchers found that “gene flow accompanied the divergence of western lowland and Cross River gorillas until just 400 or so years ago, which rather supports a scenario in which intensifying human activities may have increased the isolation of ape populations. The recent decrease in the Cross River population is accordingly most likely attributable to increasing anthropogenic pressure over the last several hundred years”(Thalmann et al., 2011). Human encroachment on Cross River gorillas natural habitat, paired with their small numbers, creates a problem of gene diversity. Unlike the
Some individuals have developed different traits to help them in the process of intra-sexual competition. The organisms with more distinctive traits have greater reproductive success. More genes of those traits are then ‘selected’ and are passed onto the offspring of the organisms. Throughout time variability in these traits becomes
Evolution is a on going process and the evolution is made up of many different processes. It allows species to become what they are, how they act, and what they will become. It also allows species to be able to survive. It produces new and different species through ancestral populations of organisms and moves them to new population. Both natural selection and genetic drift decrease genetic variation. If they were the only mechanisms of evolution, populations would eventually become homogeneous and further evolution would be impossible. There are, however, mechanisms that replace variation depleted by selection and drift (Colby).
Rantala, M. J., and Roff, D. A. 2006. Analysis of the importance of genotypic variation,
The study of the causes of substance abuse has been conflicting many people for a long time. There are two causes of substance abuse that have been argued for many years. The first cause is believed to be environmental. The second cause is a genetic cause that leads people to turn to drugs and alcohol. In “Touch of Grey” Lanthrop comes to the conclusion that his substance abuse issue posses both genetic and environmental causes. This argument is specifically compelling because he uses research and a personal statement to prove his findings. While environmental issues have a large impact on substance abuse, genetics have the greatest impact on substance abuse.
Long-term survival of a species depends on its ability to adapt to changing environmental conditions (Murphy, 1994). Genetic diversity within a species, which has taken 3.5 billion years to evolve, makes adaptations to these changing environments possible. Unfortunately, the rate of extinction of genetically diverse organisms is rapidly increasing, thus reducing this needed biodiversity, largely due to the human impacts of development and expansion. What was an average of one extinction per year before is now one extinction per hour and extinct species numbers are expected to reach approximately one million by the year 2000 (WWW site, Bio 65). As a result governmental and societal action must be taken immediately!
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By carelessly shifting around organisms, with their awesome genetic potential, we have caused major ecological disasters. Gone is the most important tree in the Northeast, the American Chestnut, our premier landscaping tree, the American Elm, and gone are huge tracts of productive fresh water marsh. Now these marshes contain only monocultures (only one species present) of purple loosestrife.
The idea of the project was to experiment breeding Drosophila Melanogaster (fruit fly) to figure out if certain genes of that species were sex linked or not (autosomal). A mono-hybrid cross and di-hybrid cross was performed. For the mono-hybrid cross, white eyed female and red eyed male were placed in one vial for them to reproduce. For the di-hybrid cross, red eyed and normal winged flies and sepia eyed and vestigial winged flies were placed in their vial to reproduce. In the mono-hybrid cross the results expected were within a 1:1:1:1 ratio. Expected results similar to the expected desired null hypothesis proposed with what the F1 parental generation breeds. The potential results would have had to have been within the ratios of 9:3:3:1. The results were clear and allowed the null hypothesis to be correct. The white eyed gene in the fruit flies is sex linked. Sepia eyes and vestigial wings are not sex linked and are examples of independent assortment.
Shreeve, jamie “Species Revival: Should We Bring Back Extinct Animals?” ngm.nationalgeographic.com 5 March 2013, 22 March 2014
Zacherl, Danielle. “Biology 171 Evolution and Biodiversity.” National Association of Research in Science Teaching 2007 Annual Meeting, New Orleans LA. (2007):n. page. Print.
Williams SE, Hoffman EA. Minimizing genetic adaptation in captive breeding programs. Biological Conservation. 2009; 2388-2400.