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bild 3 lecture 5

bild 3 lecture 5 - experiments showed all possible types of...

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experiments showed, all possible types of mutation that can happen to these bacterial genes) is always happening at a low rate in bacterial populations. Different mutations can have no effect, a slight effect, or a very large effect on the organism that carries them. Sometimes, small changes in the DNA can have a large effect, and sometimes large changes can have a surprisingly small effect. The sickle cell mutation, which we will look at in more detail later, is a single-base change with a large effect. Normal antenna Antenna converted to leg The antennapedia mutation in Drosophila. The antennapedia mutation, another small change with a large effect, is caused by a variety of small alterations in the DNA, some as small as a single base change.
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C. indicum C. ornatum C. japonense C. pacificum C . m a n k i n o i C . y e z o e n s i s 18 36 72 54 90 90 This picture shows a “polyploid series” in the genus Chyrsanthemum , in which large genetic differences, in this case increases in entire sets of chromosomes from one species to another, have a small effect. The differences in the flowers and leaves shown in the picture are actually the result of differences in individual genes, and have nothing to do with the differences in chromosome number. The Evolutionary Impact of Gene Duplication The most important mutational process that has led to increases in gene number is gene duplication , in which a second copy of a pre-existing gene is added to the genome. Initially, of course, the additional gene has exactly the same sequence as the gene from which it was derived. However, once the additional gene has made its appearance in the genome, the two genes can begin to diverge through small mutational changes that are different for each gene. Eventually, if the genes have diverged sufficiently, they can begin to take up different functions.
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Gene duplications occur repeatedly. In humans many genes now make up the hemoglobin family that specify parts of the oxygen-carrying hemoglobin molecules. These numerous genes have arisen from a single ancestral gene, through a series of chromosome duplications and gene duplications. Functions of duplicated hemoglobin genes The duplicated genes have diverged and now code for hemoglobins with different functions.
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Predominant type of hemoglobin tetramer during various developmental stages: Embryonic Fetal Adult This picture shows how the various duplicated hemoglobin genes are turned on and off during the development of the human embryo and fetus. Adult hemoglobin molecules are made up of two alpha and two beta chains, and fetal hemoglobin molecules are made up of two alpha and two gamma chains. Fetal hemoglobin evolved at the same time as the appearance of placental mammals. The fetus in placental mammals, unlike the milk-suckling fetus of monotreme or marsupial mammals, must rob oxygen from the mother’s circulation. The higher oxygen affinity of fetal hemoglobin enables it to do this.
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Duplicated genes and many other genetic changes can take place through
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