attached X A pair of Drosophila X chromosomes joined at one end and inherited as a single unit attenuator A control region at the promoter end of repressible amino acid operons that exerts transcriptional control based on the translation of a small leader peptide gene. A region djacent to the structural genes of the trp (tryptophan) operon; in the presence tryptophan this region acts to reduce the rate of transcription from the structural genes attenuator stem A configuration of the leader transcript that signals transcription termination in attenuator-controlled amino acid operons autogamy nuclear reorganization in a single Paramecium cell similar to the changes that occur during conjugation autonomous replication sequence (ARs) A segment of a DNA molecule necessary for the initiation of its replication; generally a site recognized and bound by the proteins of the replication system autopolypI a polyploid formed from the doubling of a single genome, Polyploidy in which all the hromosomes come from the same species autoradiography a process by which radioactive materials, often though not exclusively incorporated into cell structures, are located by exposure to a photographic emulsion forming a pattern on the film corresponding to the location of the radioactive compounds within the cell. A technique in which radioactive molecules make their location known by exposing photographic films or emulsions autoregulation The control of the transcription of a gene by its own gene product autosomal set The non-sex chromosomes consisting of one from each homologous pair in a diploid autosome Any chromosome that is not a sex chromosome autotrophattached X A pair of Drosophila X chromosomes joined at one end and inherited as a single unit. attenuator A control region at the promoter end of repressible amino acid operons that exerts transcriptional control based on the translation of a small leader peptide gene. A region adjacent to the structural genes of the trp (tryptophan) operon; in the presence of tryptophan this region acts to reduce the rate of transcription from the structural genes. attenuator stem A configuration of the leader transcript that signals transcription termination in attenuator-controlled amino acid operons. autogamy nuclear reorganization in a single Paramecium cell similar to the changes that occur during conjugation. autonomous replication sequence (ARS) A segment of a DNA molecule necessary for the initiation of its replication; generally a site recognized and bound by the proteins of the replication system. autopolyploid A polyploid formed from the doubling of a single genome. Polyploidy in which all the chromosomes come from the same species. autoradiography A process by which radioactive materials, often though not exclusively incorporated into cell structures, are located by exposure to a photographic emulsion forming a pattern on the film corresponding to the location of the radioactive compounds within the cell. A technique in which radioactive molecules make their location known by exposing photographic films or emulsions. autoregulation The control of the transcription of a gene by its own gene product. autosomal set The non-sex chromosomes consisting of one from each homologous pair in a diploid species. autosome Any chromosome that is not a sex chromosome. autotroph