When it comes to horizontal gene transfer, most of the new research has focused on bacteria. While they don't have what Dr. Ruth would consider sex, bacteria exchange or take in new genes in several ways. In a process called conjugation, bacteria physically interact so that DNA moves freely from one cell to another. Plasmids, which are loops of DNA independent of a bacterium's primary chromosome, move between bacteria during conjugation. Alternatively, a snippet of DNA wrapped in a piece of cellular membrane may bud off from one bacterium and be absorbed by another cell.
Bacteria can also sop up free-floating DNA, released when other cells die and break apart.
Lastly, viruses called bacteriophages, which reproduce within bacteria, can introduce genes that change their host's capabilities. The viruses inject their genes into a bacterium and force it to make new copies of the virus, which then infect other bacteria. Over time, such phage genes can integrate into a bacterium's own chromosome. May. Early on, scientists recognized that antibiotic resistance can spread among bacteria via genes located on plasmids. In the 1970s and 1980s, however, microbiologists became skeptical of the growing number of claims of horizontal gene transfer, notes Doolittle.