Lecture 6

Lecture 6 - This experiment was done by using radioactive...

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This experiment was done by using radioactive probes to search for messenger RNA coded by the gene in different tissues. The gene itself is of course present in all cells, but if it is not being expressed in a particular cell then little or no messenger RNA for that gene will be produced in that cell. This way to measure levels of gene expression, is the technique of in situ gene expression. It was also possible to demonstrate that the Bmp4 gene really is involved in beak development. The gene was inserted into the chromosome of a virus along with a regulatory region that turned it on full-blast. The virus was then injected into mesenchymal tissue of developing chicks of domestic chickens, where it caused the beak to increase greatly in size. When injected into other chick tissues it had no effect, so its expression is dependent on its location. Interestingly, the product of this gene has been found to interact with our old friend sonic hedgehog, which as we saw plays an important role in bird feather development and may play an important role in beak development as well. Are alleles at the Bmp4 gene locus involved in genetic differences between the large and small beaks of G. fortis, differences that played such an important role in the adaptation of this bird to drought conditions? Perhaps, but it is also possible that other genes with alleles yet to be discovered are involved in these differences. Nonetheless, even though the genetic differences that have been found so far only help to explain differences at the species level, it will not be long before differences are found that help to explain the phenotypic variation among individuals within the different species of Darwin’s finches. Darwinian fitness The birds that survived the drought had a higher Darwinian fitness than those that did not, because they were able to have offspring when the drought ended. We can define Darwinian fitness w as the number of offspring produced by an individual, adjusted for changes in the population size . Consider a sexually reproducing population in which the numbers of individuals do not change from one generation to the next, In such a population, the average number of offspring per individual will be one. Each member of a pair of individuals that mate for life and have two living offspring will have a w of one. If the population doubles from one generation to the next, however, then
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such a pair of individuals will have to contribute four offspring to the new generation if each member of the pair is still to have a w of one. If they were to contribute fewer than four offspring, then their genetic contribution to the new generation would be less than the average and their w would be less than one. The average value of w for the population as a whole is designated
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This note was uploaded on 07/13/2009 for the course BILD BILD3 taught by Professor Henterheather during the Spring '08 term at UCSD.

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Lecture 6 - This experiment was done by using radioactive...

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