Macronucleus structure and macronucleus development in hypotrichous ciliates.

In the course of macronuclear development of the hypotrichous ciliates all genetic information not required for normal growth of the cell is removed from the new macronucleus. This differentiation process involves DNA-splicing, excision of transposons, DNA-fragmentation, selective gene amplification and telomere addition. Since many of the processes observed during macronuclear development, such as DNA-transposition, DNA-rearrangement or selective DNA-amplification, may occur in differentiating cells of higher organisms, this biological system provides an unusual opportunity to study the ways in which DNA-sequences can be manipulated in a differentiating cell.