THE MISUSE OF MENDEL
The rediscovery of Mendel’s laws of segregation and independent assortment set genetics on a sound theoretical footing in the early 20th century. Among those that used that footing to build up a solid edifice of genetic science many have already been mentioned such as Johanson, Correns, and Punnett.
Another group that deserves special mention all worked in the same laboratory at Columbia University in New York. Under the guidance of the great American geneticist Thomas Hunt Morgan (1866-1945), a group of students that included Herman Joseph Muller (1890-1967), Calvin B. Bridges (1889-1938), and Alfred H. Sturtevant (1891-1970), studied the transmission of phenotypes cataloged by them in the fruit fly Drosophila melanogaster. From this work emerged most of the founding principles of modern genetics including chromosomal linkage and mutation.So powerful were the discoveries of the early years of the 20th century and so compelling were the models built to explain them, that some carried genetic principles to an unfortunate and, ultimately, tragic extreme. A number of scientists and nonscientists alike saw the elegant simplicity of Mendel as the answer to everything. Ignoring the complications and the exceptions that were piling up as experiments in Mendelian
genetics became more sophisticated and the traits being studied more complex, some seized upon very simple models as all that were needed to explain even the most convoluted biological characteristics. Nowhere was this more evident than in the rapidly expanding discipline of human genetics. Attracted by the allure of simplicity, some of the attempts to explain complex human traits with basic Mendelian principles are humorous when viewed from a 21st century perspective. Many of the texts of the period contained family histories that purported to demonstrate simple Mendelian inheritance of artistic ability or musical ability. One extensive pedigree displayed evidence for the inheritance of ship building skill over several generation of a Norwegian family. Another prominently showed that three generations of band directors followed a basic Mendelian pattern. It is often common even today for people to casually note that doctors or lawyers “run in certain families” and, while no one today would seriously believe that medicine or law or music or even ship building is determined by a single Mendelian gene,
such comments were taken very seriously in the early 20th century. In fact, such belief was strong enough for a field of scientific inquiry to arise that sought to enhance traits deemed to be beneficial and to eliminate traits held to be deleterious. This science was called eugenics. Eugenics comes from the Greek roots for “good” and “origin” or “generation.” The term was first used to refer to good breeding through selective heredity around 1883. By the 1920s the eugenics movement in the United States and Europe was gaining wide acceptance and was being championed by the respected American geneticist .
Charles Davenport (1866-1944). Eugenics was being portrayed as a sound mathematical science based upon Mendel’s law that could produce superior offspring via selective mating. Eugenicists held that desirable traits should be encouraged and numerous societies like the Race Betterment Foundation were established. Contests were held and prizes were awarded to “good families” at fairs and other events . The other side of the eugenics movement was much darker. The goal of promoting the inheritance of “good” traits was being mirrored by the goal of preventing the inheritance of “bad” traits. Complex human traits like alcoholism, feeblemindedness, criminality, and even poverty were attributed to a simple model of Mendelian transmission. Prevention in the United States took the form of designating certain countries and groups as being prone to these traits and banning immigration. In addition, there was a massive program of involuntary sterilization of those already here. As late as 1942 the ethics of “euthanizing” children with disabilities was seriously debated in the pages of a major medical journal. In all, thousands of American citizens and immigrants were sterilized by court order.
In Europe the eugenics movement gained equal acceptance but its power was nowhere exceeded than in Germany when it became an official policy of the Nazi Party. There, its precepts were taken to the ultimate extreme when the Nazi Party came to power in the 1930s. Soon, the list of traits to be eliminated grew quite long and “undesirables” were being rounded up and sent to camps. Selective human breeding programs, called the “liebensborn,” were established and “stocked” with young women who, by the criteria established under the Nazis, displayed the desired traits. Eventually the Nazis took this movement to the “final solution” of the question of the unfit and the concentration camps became death camps
MENDEL IN THE MODERN WORLD
The laws of heredity established by Mendel form the backbone of modern genetics. Nowhere is this more evident than in the ongoing search for genes that cause diseases in humans, animals and plants. The sophisticated, contemporary methods for mapping and, ultimately, identifying individual genes that either increase risk for developing diseases or actually cause them is firmly rooted in Mendelian genetics. Genetic linkage analysis is based upon the co-transmission of genetic material that is physically linked together on the same region of a chromosome. The mathematics of linkage analysis works because of segregation and independent assortment. A genetic marker that displays independent assortment in families relative to a trait of interest such as cystic fibrosis, Huntington’s Disease, Breast Cancer, or Alzheimer’s Disease cannot be physically linked to that trait whereas a marker that segregates along with the trait is likely to be near the gene that causes the illness. Through this method literally hundreds of human, animal and plant genes have been mapped, cloned, and studied. Indeed, while the various genome sequencing projects, including the Human Genome Project, have made this search far easier than it was just a few years ago, the initial genetic maps that were used as the guides for ordering the sequences were made using mathematical and laboratory techniques, like linkage, that are grounded in the application of Mendel’s Laws.