BY 123 Exam IV Notes - Ch 22 Evolutionary adaptation an...

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Ch. 22 Evolutionary adaptation an accumulation of inherited characteristics that enhance organisms’ ability to survive and reproduce in specific environments Evolution change over time in the genetic composition of a population (fig. 22.6) Galapagos Islands finches have arisen from an ancestral form by the gradual accumulation of adaptations to a different environment; their beaks and behaviors are adapted to the specific foods available on their home islands Descent with modification Darwin’s belief that all organisms are related through descent from an ancestor that lived in the past; then, as the descendents of that ancestral organism spilled into various habitats over time, they accumulated diverse modifications, or adaptations, that fit them to their specific ways of life (fig. 22.7) fossil record supports “descent with modification” (fig. 22.8) if all offspring survived to reproduce successfully, population would increase exponentially; this is b/c species have the potential to produce many more offspring than will eventually survive to reproduce themselves However, populations tend to remain stable in size b/c of limited resources (fig. 22.9) members of a population vary extensively in their characteristics; this is heritable, and can be acted on by natural selection Environment also selects for beneficial traits making it more likely that organisms with them will survive to reproduce (fitness) Genetic variation also comes from meiosis, sexual reproduction, mutations, bacterial gene transfer, etc. (fig. 22.10) artificial selection leads to many different variations of an original organism Broccoli, cauliflower, cabbage, Brussels sprouts, kale, and kohlrabi have all been obtained by artificial selecting heritable traits from the wild mustard plant Artificial selection modification of a species by humans over many generations by selecting and breeding individuals that possess desired traits (fig. 22.13) HIV has developed resistance to the drug, 3TC, which was designed
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to interfere with reverse transcriptase (RT), the enzyme HIV uses to copy its RNA genome into the DNA of the human host cell; the 3TC molecule is similar in shape to the cytosine [C]-bearing nucleotide of DNA, HIV’s RT picks up a 3TC molecule instead of a C-bearing nucleotide and inserts the 3TC molecule into a growing DNA chain, terminating further elongation of the DNA and thus blocking reproduction of HIV The 3TC-resistant varieties of HIV carry slightly different versions of RT that are able to discriminate between the drug and the normal C-bearing nucleotide The viruses that carry these genes have no advantage in the absence of 3TC; they actually replicate more slowly than those that carry the common form of RT; however, once 3TC is added to their environment, it becomes a powerful selecting force, favoring reproduction of resistant individuals There are two key points to natural selection Natural selection is more a process of editing than creative mechanism; a drug
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BY 123 Exam IV Notes - Ch 22 Evolutionary adaptation an...

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