Given that our current understanding of the mechanisms of inheritance has undergone major revisions over the past fifty years, I thought a brief review of our current knowledge was in order.
As complex multicellular organisms we know that we have genes for specific traits such as eye color that are predictably passed on to our offspring. This occurs through the processes of sexual reproduction which endow our offspring with a mixture of those genes carried by the two parents.
Cloning (or asexual reproduction) occurs when the offspring are identical to a single parent. In this process there is no mating and mixing of genes. Cloning is a common (but often not the only) means of reproduction in some plants, insects, bacteria, and viruses. Cloning has also been induced artificially in the laboratory by manipulation of the egg cells of higher organisms such as mice and sheep.
Under certain natural conditions, a bacterium can donate some genes to a neighboring bacterium thus changing not only the recipient bacterium but the recipient bacterium’s future progeny as well. In this way new genes (such as for antibiotic resistance) can spread through a bacterial colony very rapidly. In the sense that there is now a mixture of genes in an individual bacterium that came from two different individuals, the results are similar to that following sexual reproduction in higher organisms.
Likewise, when two different viruses infect the same cell they may exchange genes and, if they do, their offspring may emerge having different characteristics from that of either of the parent viruses. Finally, as described previously in this column (and reminiscent of some ancient myths), on rare occasions an organism can either ingest, or become infected by, another organism which, while remaining mostly intact, ends up living permanently in the host organism and replicating in concert with its host, thus producing a novel hybrid organism.