Throughout chapter one of the book, Sean Carroll mentions two distinct ways in which mutations can arise (specifically p 33). A simple manner is single-letter mutations, where letter by letter genes are changed, creating different genes, creating different proteins, creating different phenotypes, creating selective advantages. Another mode by which genetic mutation can occur is by entire segments of genetic material relocating themselves within the genome, through transposition (in other words, these genes are transposons). We see this latter type in the development of the antifreeze gene, coding for proteins that prevent the icefishes' blood from freezing.
Given your knowledge of the various effects of different types of genetic mutations, discuss the possibilities and implications that follow with each type of mutation.
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Transposons could lead to quicker "evolution" of certain genes just by "cutting and pasting" in a certain sequence wherever it is needed to change the phenotype. But transposons are also considered mutagens, leading to a higher risk of causing harm to the genome it is inserted into. When the transposon is taken out, the leftover gap is affected and may not be repaired properly, destroying that cell as well.
ReplyDeleteSingle cell mutations have a lower risk factor because the "evolution" is taking place gradually. These mutations would take longer because redundancy in the genome results in multiple triplets coding for the same protein. So to change a phenotype, many mutations may have to occur. Gradual changes allows for the best, lasting traits to be formed, thereby increasing the organisms chance of survival.
The effect of a mutation can vary greatly. Carrol states that everyone has roughly "175 new mutations" which can include changes to single neucleotides or entire blocks of DNA. Some mutations can cause huge changes in a human (often detrimental), because removing a letter from the DNA will result in an inability to produce necessary proteins (since the amino acids that make up proteins are read off in 3-letter codons, removing a single letter shifts the entire code and results in totally different amino acids). Most mutations, however, are harmless or change little. As we learned in class, introns are noncoding regions that make up most of our DNA: thus, mutations that occur on introns have no effect.
ReplyDeleteGenerally, we think mutations are dangerous: they cause genetic diseases such as cystic fibrosis. However, some mutations may provide coding for different proteins that might put an individual at an advantage in a stressful environment. The cooling of the southern oceans put environmental stress on fish. Many Antarctic fish evolved antifreeze proteins, which were probably the result of chance. One fish probably just mutated and began producing antifreeze that helped it survive much better in cold water than its buddies. Eventually, its buddies and their offspring died while this mutant fish's survived the cooling water. We generally assume that large mutations will always have terrible effects. This example of transposition instead shows that moving large chunks of DNA can be beneficial. Thus, we can see that a mutation, no matter the size, can have almost any effect on an organism.