The Foundation of Genetics. The traditional foundation of genetics, and therefore of medical genetics, dates from the 1900 "rediscovery" of Mendel's papers (Dunn, 1965). Between the years 1902 and 1909, several additional, clarifying terms were defined by the "founder of genetics" William Bateson (1861-1926) and his colleagues; these included cornerstone concepts such as genetics, segregation, P1, F1 and F2, allelomorph (allele), homozygosity and heterozygosity, epistasis, and indeed Mendelism itself.
Working with R. C. Punnett in 1906, Bateson reported the first exceptions to Mendel's second principle (independent assortment), and thus demonstrated the first case of trait linkage (in the sweet pea).
American geneticist Thomas Hunt Morgan (1866-1945) and his students discovered chromosomal rearrangements such as inversions and translocations, mapped the first genes to chromosomes, and deduced the earliest linkage groups. Members of this research group both discovered and caused new (de novo) morbid mutations in the Drosophila genome.
"Inborn Errors of Metabolism." The English physician Archibald Edward Garrod (1857-1935), in collaboration with Bateson, first applied Mendel's principles to a human condition, alkaptonuria (see Table 1 of the entry Genetic Disease II). They concluded that alkap-tonuria was a monogenic heritable genetic disease, and that it was a classic example of Mendel's autosomal recessive mode of inheritance. Garrod was later to show that albinism and other genetic conditions behaved in a similarly predictable manner. Garrod's famous phrase, "inborn errors of metabolism" was the title of both a 1902 paper in the Lancet, and of a landmark 1909 book.
The Rise and Fall of Eugenics. British statistician (and cousin of Charles Darwin) Francis Galton (1822-1911) believed that complex or "continuous" physical traits (in contrast to Mendel's discrete, discontinuous traits) were also heritable and could be quantified. Stature and total fingerprint ridge count are well-documented examples of such traits. Galton was one of the inventors of the "twin method" of heritability estimation (see multiple births in Table 1 of the entry Genetic Disease II). Galton was the first, in 1889, to describe degrees of genetic similarity, then known as Galton's law, which states that in bisexual lineages (such as in humans) each individual receives, on average, one half of his or her inherited characteristics from each parent, one quarter from each grandparent, one eighth from each great grandparent, and so on.
In addition to these productive discoveries, Galton was also an outspoken advocate of the application of useful scientific information to human affairs, and to this end he coined the term eugenics. Eugenics is the controversial study of cultural mechanisms that may improve (or impair) the hereditary physical or mental qualities of future generations of human populations. One of its earliest advocates was geneticist Charles Benedict Davenport (1866-1944), an outspoken leader of the American eugenics movement. Although well intended— it sought to remove all forms of genetic disease from society—this international movement suffered from a choice of traits with complex inheritance, including some with large environmental factors (e.g., "feeblemindedness"), and from controversial legal and political applications (compulsory sterilization, genocide). Thus its influence in America was fleeting, and much of its conceptual vocabulary and rationale has been ignored.
Molecular Genetics. Molecular geneticists study heritable systems at the chemical level, and attempt to understand the control of metabolic processes, including regulatory processes, by genes and gene products (Collins & Gelehrter, 1992). One of the first major steps in this endeavor occurred in 1949 when Linus Pauling and colleagues showed that structural changes ("sick-ling") occurred to the red blood cells of individuals with SCD. Subsequent to the crucial work of Rosalind Franklin, and of the follow-on description of the structure of DNA by James Watson and Francis Crick in 1953, Pauling was able to describe the first substitutional mutation in humans. In 1964 Pauling reported the displacement of one amino acid (glutamic acid) by another (valine) at sequential position six in the beta chain of adult hemoglobin—the exact substitutional mutation responsible for the sickle cell allele. Pauling coined the term "molecular disease" to stand for this new level of etiological description.
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