Methodology in Basic Genetics

By Walter J. Burdette | Go to book overview

William Hayes, Sc.D., F. Jacob, M.D., D.Sc., and E. L. Wollman, M.D., D.Sc.


CONJUGATION in BACTERIA

"We have now fashioned our bricks from the primitive clay and the next job is to build with them."

Sir Arthur Eddington, "The Nature of the Physical World."

Genetic recombination in bacteria may be mediated by transformation, transduction, or conjugation. All these ways of achieving recombination have two features in common. In the first place, genetic transfers occur unidirectionally from donor to recipient bacteria in all cases. Second, only a fraction of the genetic material of a donor cell is transferred to a recipient which, on the other hand, contributes its cytoplasm as well as its entire genome; the recipient cell thus becomes a zygote that is incompletely diploid. Zygotes of this sort are termed merozygotes,1090 and it is obvious that, in them, the potentiality for recombination is limited to the diploid part of the genome so that the recipient genotype predominates among the recombinants.

The main distinguishing features of the three systems concern the way in which differences between donor and recipient bacteria are determined and the size of the donor fragment which is transferred. In both these respects, conjugation is more akin to true sexuality, since the differentiation into donor (male) and recipient (female) types that it displays is genetically and physiologically determined, whereas the genetic contribution of the donor to the zygote is usually much greater than in transformation or transduction and may be complete. Thus the system of conjugation is well adapted to providing information about the nature and organization of the bacterial chromosome as a whole as well as to the study of nuclear-cytoplasmic interactions.

Although conjugation has been demonstrated in several bacterial species, this account will be restricted to the E. coli K12 system, the only one that has been extensively

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