GENETIC DETERMINATION OF HIGH MEIOTIC REVERSION FREQUENCIES IN ISOLEUCINE-VALINE 1 HOMOALLELIC CROSSES INNEUROSPORA

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Abstract
High frequency reversion in homo- and heteroallelic crosses of isoleucine-valine-1 (iv-1) group 2 alleles was reported previously. The genetic determination of homoallelic reversion in a single allele, Tiv 318, is reported here.The property of yielding prototrophs in test crosses underwent 2:2 segregation in tetrads and showed close linkage to spray (sp) and actidione-2 (act-2). Crosses of ordered segregants from a reverting lysine-1 (lys-1) iv × iv sp cross and of random spore isolates from six reverting lys-1 iv × iv act-2 crosses identified a disparity of origin of the pertinent chromosome region as an enhancing factor, but not a sine qua non of reversion. This region exists in at least three states such that a combination of two is effective. Direct involvement of outside markers was excluded. The cytogenetic nature and mode of operation of the enhancing factor are unknown.Prototroph frequency did not differ in reciprocal crosses, and the growth rate of revertants was unaffected by isoleucine and valine.

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