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Title: Genetics Question: Mapping Genes and Coefficients of Interference for trihybrid test-cross? Post by: smile92 on Aug 12, 2012 I have a practice problem to study for my genetics exam. The problem follows as below:
Test-crossing a trihybrid Drosophila female produced the following results: Progeny: +++ 2 abc 1 +b+ 24 a+c 23 ++c 39 ab+ 38 +bc 436 a++ 437 total progeny: 1000 Map these genes and determine the coefficient of interference. Any help would be appreciated. Thanks! Title: Genetics Question: Mapping Genes and Coefficients of Interference for trihybrid test-cross? Post by: oakaniru on Aug 12, 2012 These are the steps:
1) Decide the parental types (biggest numbers) and double crossover types (smallest numbers) Parental types: +bc and a++ dco types: +++ and abc 2) Determine the gene in the middle based on the parental and dco types. The gene in the middle is a 3) Re-arrange the gene order: +++ 2 bac 1 b++ 24 +ac 23 ++c 39 ba+ 38 b+c 436 +a+ 437 4) Determine single crossover in region I (scoI) and in region II (scoII) based on the parental types: scoI: ba+ and ++c scoII: b++ and +ac 5) Calculate distance between b-a (region I) and a-c (region II) Between b-a = (scoI + dco)/total x 100 = (38+39+2+1)/1000 x 100 = 8 mu Between a-c = (scoII + dco)/total x 100 = (24+23+2+1)/1000 x 100 = 5 mu 6) The map is b<----8---->a<---5-->c 7) Interference, I = 1 - c, where c is coefficient of coincidence c = (observed dco)/(expected dco) obs dco = 3/1000 = 0.003 exp dco = 0.08 x 0.05 = 0.004 c = 0.003/0.004 = 0.75 --> I = 1 - 0.75 = 0.25 |