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Unformatted text preview: 5.3.2007 • In previous example about deafness, you see a difference in 9:3:3:1 ratio and it is because they must have a functioning gene product in both A and B, either homozygous dominant or heterozygous for both o Compare this to the readings when you get a 15:1 ratio etc. and why each happens Pleiotrophy: One gene produces multiple seemingly unrelated phenotypic effects • Duchenne musc • Calves look very buff but it is due to swelling from collecting waste products from breaking down the muscle bundles, this is not Pleiotrophy, misunderstanding is when you list off of a bunch of symptoms caused by a mutation at a particular gene, because it isn’t hard to figure out that swelling in some muscle and weakness in another are related, • Instead Pleiotrophy is when it is suprising, when it is seemingly unrelated ex: mental retardation of a mild degree in Duchenne gene when there is also the characteristic prximal muscular dystrophy • Dystrophin product is necessary for the functioning of different types of cells, it protects muscle bundles from damage and breakdown over time, if this product is not there you get deterioration of the muscles • The product is also necessary in brain tissue and to protect and support, without it brain function can be compromised as well…so its not that the effects are unrelated they just seem unrelated on the surface Variable expressivity • Variation in phenotype among those with the same genotype • In compound heterozygotes people have the same condition and some of them can still have different phenotypes, and then some of them are due to different genotypes • But this is different, this is the same genotype and different phenotypes (noticeable differences) this is variable expressivity. Same genotype and it is manifested in different ways. • Different symptoms o Osteogenesis imperfecta: bone development gone wrong, causes bones to be very brittle and prone to breakage Can cause deafness Whites of the eyes to be blue (blue sclera) It is dominant, so take the most common mutant allele causing it and put it with the wild type allele (most common wild allele) and just those individuals that have that genotype…even among them some will have just the blue sclera, some will have blue sclera and brittle bones, some will have blue sclera and deafness, some will have all three • They all have the same genotype at that gene, what is the difference? Environment • We have a little over 20,000 protein encoding genes and these people have the same genotype at only one of those, so all these other genes could be interacting to cause the difference in phenotypes. This is NOT EPISTASIS. Other genes have to do with how bones are formed, not having major influences but genes could have minor effects on regulation of the one gene we are talking about…all of these reasons attribute to the varying phenotypes when combined with the same genotype at the osteogenesis imperfecta gene • Background genotype: have a small effect but cumulatively can affect it in a larger scale...
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- Spring '08