[Localization of some highly mutable loci of Antirrhinum majus L. by linkage studies].

1. Three new spontaneous mutations of the caeca-type (reduction of yellow flower pigments) were found to be homologous, but are not alleles of the authentic caeca locus. However, two new graminifolia mutations are alleles of the authentic gram locus. 2. Six loci, characterized by a high frequency of forward mutation, were studied, three are located on the gram-chromosome. This chromosome thus contains six unstable loci: graminifolia, incolorata-II, incolorata-III, silvescens-II, caeca-I and fimbriata. 3. The gene-sequence of the gram-linkage group is: del - inc.-III - gram - silv.-II - cen - inc.-II - cae.-I - fim. 4. The loci of incolorata-IV and silvescens-I were localized in the uni-chromosome. Both of them occasionally exhibit greatly increased crossing-over exceeding the 50 percent limit. It is assumed that compensated gametic lethals are the cause of this phenomenon.