141Problemsalternative b were correct, because crossovers on eitherside of the centromere would generate the MIIpatternsfor the nicand the adloci independently.Is the map distance from nicto adsimply 9.3025.0554.25 m.u.? Close, but not quite. The best way ofcalculating map distances between loci is always bymeasuring the recombinant frequency (RF). We couldgo 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, andthe NPD asci are classes 2 and 6.Hence,percent, or 5.2 m.u.,and a better map is5.05 m.u. 5.2 m.u.10.25 m.u.nicadRF1[12(100)12]/100055.2RF512T1NPDThe reason for the underestimate of the ad-to-centromere distance calculated from the MIIfrequencyis the occurrence of double crossovers, which can pro-duce an MIpattern for ad, as in ascus type 4:nic1nic1nicnicnic1 adad1ad1adnic1nicnicnic1nic1nicnicadadadadad1ad1ad1ad1PROBLEMSBASICPROBLEMS1.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.