Introduction to Genetic Analysis 142

Introduction to - 44200_04_p115-150 11:53 AM Page 141 Problems 141 alternative b were correct because crossovers on either side of the centromere

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141 Problems alternative b were correct, because crossovers on either side of the centromere would generate the M II patterns for the nic and the ad loci independently. Is the map distance from nic to ad simply 9.30 2 5.05 5 4.25 m.u.? Close, but not quite. The best way of calculating map distances between loci is always by measuring the recombinant frequency (RF). We could go through the asci and count all the recombinant as- cospores, but it is simpler to use the formula . The T asci are classes 3, 4, and 7, and the NPD asci are classes 2 and 6. Hence, percent, or 5.2 m.u., and a better map is 5.05 m.u. 5.2 m.u. 10.25 m.u. nic ad RF 1 [ 1 2 (100) 1 2] / 1000 5 5.2 RF 5 1 2 T 1 NPD The reason for the underestimate of the ad -to- centromere distance calculated from the M II frequency is the occurrence of double crossovers, which can pro- duce an M I pattern for ad , as in ascus type 4: nic 1 nic 1 nic nic nic 1 ad ad 1 ad 1 ad nic 1 nic nic nic 1 nic 1 nic nic ad ad ad ad ad 1 ad 1 ad 1 ad 1 PROBLEMS B ASIC P ROBLEMS 1. A plant of genotype
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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