O. fallax contains in its one cell both a micronucleus (MIC) and a macronucleus (MAC). The MAC develops from a mitotis sister of the MIC in the genetically new individual. Once equipped with its new MAC the cell grows clonally. The MAC provides most or all RNA needed for clonal life. The MAC DNA genome consists of about 1000 copies each of 20,000 different, short linear duplex DNAs and carries only 10% of the germline (MIC) sequence complexity. As expected, analyses of cloned MIC DNA regions carrying MAC-destined sequences show MIC-limited sequences between blocks of sequences destined to be on different MAC pieces (inter-MAC). Such analyses also show MIC-limited sequences separating blocks of MAC-destined sequences which are contiguous on the same piece of MAC DNA (intra-MAC), analogous to introns or intervening sequences embedded in genes; this is not a rare phenomenon but has been seen at every MAC-homologous locus we have examined. We will study the sequence rearrangements (involving inter- and intra-MAC sequences) which give rise to separate MAC pieces lacking intervening MIC-limited sequences. All MAC pieces carry dC4A4C4A4C4 at both termini, which we now view as telomeres: this sequence is found at MIC chromosome telomeres as well as internally in MIC DNA at boundaries of inter-MAC blocks; ciliate MAC termini are known to act as telomeres in yeast. To learn how MAC telomeres are generated we will further study inter-MAC boundaries, as well as more fully characterize both MIC and MAC telomere structures. Many MAC pieces belong to small families which appear to arise as products of alternate processing of single MIC loci. We will more fully characterize this phenomenon and perform studies to learn what role such families play. We have characterized a MAC DNA piece, the ploidy of which is modulated during MAC development. What is the role of this DNA and how can the modulated during MAC development. What is the role of this DNA and how can the modulation be manipulated? Several fundamental characteristics of O. fallax practical biology, of MAC development, and of MIC and MAC DNA will be determined. Inter-MAC and intra-MAC related genome rearrangements which we observe as a matter of course seem strongly relevant to genome rearrangements controlling the immune system and to oncogene-related Robertsonian rearrangements in cancer etiology (telomeres dictate the rules of Robertsonian rearrangments). We argue that somatic genome rearrangements may yet be discovered in a wide variety of developmental paths. Alternate juxtapositioning of sequences likely plays a major role in the control of gene expression in man and his viruses.