The CL-repeat is a repetitive sequence that is unique to the maize B chromosome, where it resides in the centromeric knob and the first 3 distal heterochromatic regions of the long arm. Given this organization, it would be desirable to identify molecular markers that are specifically distributed in the B chromosome. In this report, the CL-repeat has been used to develop a class of molecular markers for the maize B chromosome. To this end, a modified transposon display procedure designated as CL-repeat display was used to generate and display 26 genomic fragments that are specific to the B chromosome, all of which were cloned and sequenced. The sequences of 19 fragments were highly homologous to the 5′ or 3′ terminus of the CL-repeat. Five of these fragments also contained sequences that were homologous to sequences of the B chromosome centromere. Four of the other 7 fragments shared homology with B chromosome centromere sequences, and the remaining 3 were of unidentified sequences. Using 13 B-10L translocations with various breakpoints along the B chromosome long arm, the 26 CL-repeat display markers were mapped to definite regions of the B chromosome. This strategy should be feasible for the development of molecular markers for the B chromosome in maize and in other species where B chromosome-specific repeats have been identified.
ABSTRACT. The papaya (Carica papaya L.) is one of the most important economic tropical fruits in the world, and the hermaphrodite is the preferred type in field cultures. We analyzed the sexual ratio of offspring from the cultivar 'Taiwan Seed Station No. 7' (T7) by a selfcross and its cross with Taichung Sunrise (TS). Female progeny from the T7 self-crossing were not observed. This finding may be caused by a lethal gene that is linked to females. In this study, we selected 192 simple sequence repeats (SSRs) to analyze the polymorphism between T7 and TS. A total of 37 SSRs were identified for T7 and TS. In addition, 14 SSRs served as the molecular makers for identification Hermaphrodite papaya genetic analysis and SSR marker development of T7, TS and their hybrid offsprings. Thus, the results show that the genetic similarity between T7 and TS is rather high. This suggests that T7 may be a mutant of TS. Phylogenetic analysis from the SSR polymorphisms of the above parent strains and 15 F 1 offspring revealed the genetic distance of the F 1 offspring located between T7 and TS. The results of this study may provide an opportunity for elucidating the genetic characteristics of all hermaphrodites via identification of molecular makers.
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