CYTOGENETICS OF GENOMIC EXCLUSION IN TETRAHYMENA

Abstract

ENOMIC exclusion is an abnormal form of conjugation that has been observed in syngen 1 of Tetrahymena pyriformis In crosses of certain clones of a strain to normal clones of other strains, only the genes derived from the normal parent appeared in the progeny, although both exconjugants were recovered, and both were diploid and identical in phenotype. Partial insight into the nuclear basis of genomic exclusion came from the results of a cross of C*, an abnormal clone of the inbred C strain, and a normal clone from the AB strain, heterozygous for H serotype alleles distinct from those found in strain C Only alleles derived from strain AB were recovered in the progeny, and the progeny were distributed among three phenotypic classes in an approximate 1:2:1 ratio. This observation suggested that two meiotic products from the AB parent united to form the syncaryon.