bild 3 lecture 8

bild 3 lecture 8 - It is likely that competition between...

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It is likely that competition between larvae with the same genotype bring about this frequency dependence, with sitters battling it out with sitters when they are common and rovers battling it out with rovers when they are common. But if so, why should intragenotype competition be stronger than intergenotype competition? Detailed observations of larval behavior are needed to confirm or reject this hypothesis. Studies of the effects of homologs of the for gene in other organisms will cast much light on how differences in their behaviors have evolved. Recently, the expression of the for gene has been studied in honeybees. Worker bees spend the first few weeks in the hive, and then begin to forage for food outside. It has been shown that the for gene is expressed at low levels during the young workers’ time in the hive, and then shifts to higher levels when they leave the hive. Bees that are still in the hive show lower levels of for activity than bees of the same age that have begun to forage. More recently, it has been shown that this Amfor gene (Apis melifera for gene) is involved in phototaxis — the bees that begin to express the gene respond more readily to light, perhaps
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encouraging them to leave the hive. It is not yet known whether the Drosophila for gene affects phototaxis in the same way as the bee gene. The for gene’s influence on behavior can be expressed in other ways in different species. In red harvester ants, the for gene is turned off rather than on when the young ants leave the nest, exactly the opposite of its pattern of expression in bees! The Importance of Balanced Polymorphisms If a population possesses a great deal of balanced genetic polymorphism that affects fitness, then it will have the capacity to undergo rapid changes as a result of selection. Such a population can quickly adapt to changes in the environment, even extreme changes such as the drought that killed most of the bird population of Daphne Major. In addition to selection and mutation, other factors cause allele frequencies to change over time. These factors are genetic drift and gene flow. 3) Random Genetic Drift As populations of organisms reproduce, allele frequencies fluctuate from one generation to the next. These fluctuations can have many causes, but one of the most important is the fact that, entirely as a result of chance, alleles do not have an equal probability of being passed to the following generation. Such random fluctuations of allele frequency were named random genetic drift by Sewall Wright. It is impossible to predict what will happen to an individual allele as a
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This note was uploaded on 11/05/2008 for the course BILD BILD 3 taught by Professor Woodruff during the Spring '08 term at UCSD.

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bild 3 lecture 8 - It is likely that competition between...

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