Q27

MORSE, M. L., University of Wisconsin, Madison, Wis.
--Cis~trans position effect in transduction heterogenctes
of Escherichia coli.--(ha phage Lambda can transduce a
Chromosome fraguen’ which includes a cluster of genee for
galactose fernentation. Most of the transformed clones —
are "diploid" er heterogenotic for the transduced genes.
Many combinations of non-allelic Gal- mutants give galace
tose positive heterogenotes as readily as Gal+/Gale,
However, some combinations of Gale gave smaller and delayed
yields of positive clones. Further analysis disclosed a
cis-trans position effect between certain loci. For exe
ample, while the cis ++/-— heterogenotes formed by trans-
duction from Gal,+0al),+ to Gal,~Gal)- are positive, the
trans +~/.+ heterogenotes from the transduction fren
Gal;+Galj,- to Galj-Gal),+ are phenotypically galactege
negative, In the negetive clones, positive heterogenotes
axe later formed by crossing over in occasional colle,
Further segregation results in all possible haploid combi-
nations, +=-, -+, ++, and ~«, The delayed ylelds that were
observed initially are based on these secondary events.
Reciprecal transductions have given identical phenotypes,
so that in heterogenctes the genes in the fragment are
functionally equivalent to the homologeus genes in the
chromosome, The galactose positive phenotype thus requires
that + alleles be in adjacent positions either in the frag-
mont or the chromosome.

Reprinted from Genetics, )0:586=587, 1955.