BIOL 3333 1st Edition Lecture 10 Modifications of Dihybrid Mendelian Ratios- Caused by Gene InteractionsGene interaction: can lead to differences in phenotypic expression from that which is expected in the absence of such interactionsEpistasis: - the literal meaning is to “stand upon” - this is where one gene can modify the phenotypic expression of a non allelic gene when both genes are present in the genome In chickens: 4 separate comb phenotypes:- walnut- rose- pea- single How do they occur:-both rose and pea are dominant to single! F1 walnuts are crossed with one another: Walnut x Walnut and would yield:9 Walnut: 3 Rose: 3 Pea: 1 Single Suggests that: dihybrid cross with 2 separate genes are interacting in these phenotypes Model for Comb Phenotype in chickens: These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Both of these combinations will yield a comb phenotype Complementary Gene Action: dihybrid has a different phenotypeand different genes are involvedModel for Complementary Gene Action:-dominant allele at both the A and B loci-necessary to get to phenotype Z-yields 9/16 A_B_ = PURPLEand 3/16 aaB_ + 3/16 A_bb + 1/16 aabb = WHITEDuplicate Gene Action:Example of Duplicate Gene Action: Flower Shape in Shepherd’s Purse: Heart x Narrow -> Heart x Heart -> 15 heart: 1 NarrowModel for duplicate gene action:- Having is a dominant allele at either the A or B locus is sufficient to get to phenotype Z - Any dominant allele willgive Z phenotype- Only the aabb genotypewill be insufficient - This is a 15:1 ratio- There is unequal crossing over here:Model for Dominant Epistasis:- a dominant allele at the B locus will block phenotype Y - a dominant allele at the A locus will lead to phenotype Z Example: Fruit color in squashModel for Recessive epsistasis: black pigmentbrown pigmentYields: 9/16 C_B_ = black3/16 C_bb = brown3/16 ccB_ = white1/16 ccbb = white 9 black: 3 brown: 4
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