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4 Extensions - Extending Mendel's Basic idea This lecture...

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Extending Mendel’s Basic idea This lecture shows a number of examples illustrating the power of Mendel’s basic idea to a number of more complex systems The general concepts are important, NOT the particular details for each system Basic Concepts Some alleles can be lethal Multiple alleles ABO blood groups Interaction between alleles at the same locus (dominance) Interaction between alleles at different loci ( epistasis ) Modifiers and supressors Penetrance vs expressivity The mystery of yellow mice One of the early tests of Mendel’s (rediscovered) results with Lucein Cuenot’s work on the yellow allele in mice Yellow X non-yellow -> 50% yellow, 50% non- yellow Yellow X Yellow -> 2/3 yellow, 1/3 non-yellow No pure-breeding yellow strains found! How can we account for these ratios? William Castle (1910) offered the solution: Yx -> yellow, YY -> lethal!
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The mouse yellow allele is an example of pleiotropy: an allele influencing two (or more) traits Here coat color, viability The Manx gene is cats is another example of an allele lethal as a homozygote Mm = tailess, MM = dead The environment can influence the phenotype of an allele The Himalayan allele in rabbits is an example of a temperature-sensitive (ts) allele The Himalayan allele makes a pigment
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