BIOL 2050 lecture 4 - Mendelian genetics Part 2 BIOL 2050...

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9/20/2011 1 Mendelian genetics Part 2 BIOL 2050 Lecture 4 Hybrids are formed when individuals with different forms of the same trait cross Progeny can be predicted using either punnett squares or probability calculations Traits can be: - dominant or recessive (e.g. Huntingtons disease) - incompletely dominant (e.g. snapdragon colour) - codominant (e.g. blood type) Recapping yesterday... Dihybrid crosses Crossing individuals that differ by two characteristics Do alleles behave independently? Example using seed colour (yellow or green) and seed shape (wrinkled or round) What if we want to look at more than one trait?
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9/20/2011 2 Dihybrid crosses What if we want to look at more than one trait? Dihybrid crosses Mendel always obtained the ratio 9:3:3:1 - 9/16 round and yellow (both dominant traits) - 3/16 wrinkled (recessive) and yellow (dominant) - 3/16 round (dominant) and green (recessive) - 1/16 wrinkled and green (both recessive traits) Alleles were independent of each other What if we want to look at more than one trait? Principle of independent assortment Principle of independent assortment Alleles at different loci separate independently of each other Only applies to loci on different chromosomes , not to genes located close together on same chromosome Extension of the Principle of Segregation
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9/20/2011 3 Due to independent assortment probability calculations for dihybrid crosses are simple Dihybrid crosses and predictions Punnett square Punnett square still usable, but more complicated What if you wanted to predict outcome of crossing four traits? RrYYGGtt Alternative is branch method Branch method
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