. Cell heredity. Cytogenetics. 134 CELL HEREDITY. FIGURE The U-tube used to show that cell contact is required for bacterial re- combination. Sintered glass disc which allows passage of medium but not of bacteria form cells with a capsule of type b, sometimes yielding ah transformants with both antigens in their capsules. The association of the two DNA's is usually retained so that the DNA extracted from the doubly encapsu- lated types sometimes gives linked transformations; but the coupled marker genes may also separate so that cells are transformed for one or the other. MATING IN BACTE
. Cell heredity. Cytogenetics. 134 CELL HEREDITY. FIGURE The U-tube used to show that cell contact is required for bacterial re- combination. Sintered glass disc which allows passage of medium but not of bacteria form cells with a capsule of type b, sometimes yielding ah transformants with both antigens in their capsules. The association of the two DNA's is usually retained so that the DNA extracted from the doubly encapsu- lated types sometimes gives linked transformations; but the coupled marker genes may also separate so that cells are transformed for one or the other. MATING IN BACTERIA Some bacteria, such as E. coli, may exchange their genes by a mechan- ism which involves cell contact. Many different lines of investigation show that this mechanism does not involve either virus or free nucleic acid molecules; no filterable agent is necessary. For example, a U-tube is used with a bacterial filter at the base separating the two arms (Figure ). In each of these arms is a suspension of E. coli of a different genotype. By alternatelv applying pressure to the air above the suspen- sion in each arm, the liquid is forced through the filter in both directions and mixed. But the bacteria cannot pass through, and each type re- mains separated. Under these conditions, recombination is never ob- served. It only occurs when the two strains are in the same suspension. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sager, Ruth; Ryan, Francis J. (Francis Joseph), 1916-. New York, Wiley
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