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Pleiotropy - for enzyme 2 prevents the expresson of the...

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Pleiotropy Genes that affect more than one trait are called pleiotropic. For example, people with Marfan syndrome may be tall, thin, have long legs, arms and fingers, and may be nearsighted. Their connective tissue is defective. If unrepaired, the connective tissue surrounding the aorta will eventually rupture and kill the person. All of these characteristics are due to a single gene. Epistasis Alleles at one locus prevent the expression of alleles at another locus. This interaction is referred to as epistasis. Example: Flower color in peas enzyme 1 enzyme 2 AA or Aa BB or Bb compound A → compound B → red pigment An individual with AA or Aa genotypes will have red flowers. AA or Aa individuals could have white flowers if the individual also has a "bb" genotype (example: AAbb). In this case, the locus
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Unformatted text preview: for enzyme 2 prevents the expresson of the locus for enzyme 1. Genomic Imprinting sometimes an allele is expressed differently if it is inherited from the mother than if it is inherited from the father. Example: Huntington's disease is expressed earlier if inherited from the father. The symptoms of Huntington's disease are caused by a slow deterioration of brain cells that begins at middle age. It is characterized by involuntary jerking movements of the body including facial muscles and slurred speech. Later, there is difficulty swallowing, loss of balance, mood swings, impaired reasoning, and memory loss. The person eventually dies, usually to pneumonia or heart failure. Polygenic Inheritance A polygenic trait is due to more than one gene locus. It involves active and inactive alleles. Active alleles function additively....
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