The genetic exchange between bacteria (conjugation) was demonstrated by light microscopy. Conjugation occurs with bacteria possessing a gene that enables frequent recombination. Bacterial DNA transfer occurs in one direction only while chromosomal material is introduced into a \u201cfemale\u201d cell. The so called male and female cells of e.coli differ in the presence of a fertility factor (F). When F+ and F- cells are mixed together, conjugal pairs are formes with attachment of male (F+) sex pilus to the surface of an F- cell.