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Unformatted text preview: The Bombay phenotype in humans is caused by an absence of the H antigen so that the ABO phenotype will be O no matter what the ABO genotype. A soap opera example of this is given on page 89 (figure 5.4) in Lewis. Pleiotropy Mutations in one gene may have many possible effects. Problems in tracing the passage of a mutant allele through a pedigree can arise when different members of a family express a different subset of the symptoms. In the case of Tuberous sclerosis , an autosomal dominant condition affecting about 1 in 6000 people in the UK, symptoms can include any subset of: o small depigmented patches on the skin o a disfiguring facial rash o kidney cysts o heart tumours o mild to severe mental subnormality o autism among others. Lewis gives the interesting example of Tourette syndrome which may cause strange behavioural problems. Pleiotropy can occur whenever a gene product is required in more than one tissue or organ....
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