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Classical Genetics: Foundations

Mendel, Gregor. 1865. Experiments in plant hybridization. Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr 1865, Abhandlungen, 3-47. (395,699 bytes; 41 pages, no figures)

In February and March of 1865, Gregor Mendel presented the Brünn Natural History Society in Brünn, Czechoslovakia, with the results of his investigations into the mechanisms governing inheritance in pea plants. The next year, the work was published as Mendel, Gregor. 1866. "Versuche über Pflanzen Hybriden." Verhandlungen des naturforschenden Vereines in Brünn, 4:3-47.

In this remarkable paper, Mendel laid the groundwork for later became the science of genetics. However, the work was largely ignored when it appeared and Mendel moved on to other things. He died in 1884.

His work was rediscovered at the turn of the century and its significance immediately recognized. Genetics, as a formal scientific discipline, exploded into activity in 1900.

An annotated version of Mendel's paper is also available. The annotated version contains explanatory notes throughout the document. This can be useful to those reading Mendel's paper for the first time.

For those wishing to see and read Mendel in the original, a facsimile reprint edition is available. This version is in Adobe PDF format, but the pages are images of the original publication, not a new tyoe-setting of the material. This is a large file (2,142,414 bytes).

You may also with to visit The Mendel Web site, maintained at NETSPACE.ORG by Roger Blumberg. A MIRROR SITE of MendelWeb is maintained at the University of Washington. The site offers many additional resources for the Mendel scholar.

Bateson, William. 1899. Hybridisation and cross-breeding as a method of scientific investigation. Journal of the Royal Horticultural Society, 24:59-66. (89,523 bytes; 13 pages, no figures)

In this talk, given in 1899, before Mendel's work had been rediscovered, Bateson gives his vision of what kind of research will be necessary to shed light on the processes of inheritance and evolution:

What we first require is to know what happens when a variety is crossed with its nearest allies. If the result is to have a scientific value, it is almost absolutely necessary that the offspring of such crossing should then be examined statistically. It must be recorded how many of the offspring resembled each parent and how many shewed characters intermediate between those of the parents. If the parents differ in several characters, the offspring must be examined statistically, and marshalled, as it is called, in respect of each of those characters separately.

One would be hard pressed to provide a better anticipation of the experimental approach of Gregor Mendel. Small wonder that Bateson, upon encountering Mendel's work, quickly became convinced that the correct method for studying inheritance was finally at hand.

Bateson, William. 1900. Problems of heredity as a subject for horticultural investigation Journal of the Royal Horticultural Society, 25:54-61. (84,218 bytes; 12 pages, no figures)

Mendel's work of 1865 was largely neglected, until 1900 when it was simultaneously rediscovered by Hugo de Vries, Carl Correns, and Erik von Tschermak. When Mendel's work came to the attention of William Bateson (who himself had already been advocating controlled crosses as an approach to studying heredity), he was convinced that Mendel's work was of major importance:

That we are in the presence of a new principle of the highest importance is, I think, manifest. To what further conclusions it may lead us cannot yet be foretold.

Bateson devoted the remainder of his scientific career to further elucidations of "Mendelism." This present paper captures the enthusiasm of Bateson's first encounter with the works of Mendel.

Garrod, Archibald E. 1902. The incidence of alkaptonuria: A study in chemical individuality. Lancet, ii:1616-1620. (145,052 bytes; 18 pages, no figures)

This paper is a true classic. Like Mendel's own work, this report offers insights so far ahead of its time that it, and Garrod's follow-on work, were largely neglected, until later efforts to elucidate the physiological functioning of genes led to the Nobel-prize-winning one-gene, one-enzyme hypothesis.

Less than two years after the rediscovery of Mendelism and just a few years after the word biochemistry was first coined, Garrod reports on alkaptonuria in humans and comes to the conclusion that it is inherited as a Mendelian recessive and that the occurrence of mutations (sports in the word of the time) in metabolic function should be no more surprising than inherited variations in morphology.

Sutton, Walter S. 1902. On the morphology of the chromosome group in Brachystola magna. Biological Bulletin, 4:24-39. (267,350 bytes; 14 pages, 11 figures)

In this paper, Sutton reports cytological studies of grasshopper chromosomes that lead him to conclude that (a) chromosomes have individuality, (b) that they occur in pairs, with one member of each pair contributed by each parent, and (c) that the paired chromosomes separate from each other during meiosis.

After presenting considerable evidence for his assertions, Sutton closes his paper with a sly reference to its undoubted significance:

I may finally call attention to the probability that the association of paternal and maternal chromosomes in pairs and their subsequent separation during the reducing division as indicated above may constitute the physical basis of the Mendelian law of heredity. To this subject I hope soon to return in another place.

Hardy, G. H. 1908. Mendelian Proportions in a Mixed Population. Science, NS. XXVIII:49-50 (19,473 bytes; 1 page, no figures)

Every geneticist has heard of the Hardy-Weinberg Law and of Hardy-Weinberg Equilibrium, and nearly all basic biology texts teach that G. H. Hardy played a seminal role in founding population genetics. But, what most biologists don't realize is that Hardy's total contribution to biology consisted of a single letter to the editor in Science. The letter began,

I am reluctant to intrude in a discussion concerning matters of which I have no expert knowledge, and I should have expected the very simple point which I wish to make to have been familiar to biologists. However, some remarks of Mr. Udny Yule, to which Mr. R. C. Punnett has called my attention, suggest that it may still be worth making.

With that, Hardy offered his "simple point" and then washed his hands of biology. His autobiography, A Mathematician's Apology, makes no mention of population genetics.

Morgan, Thomas, H. 1909. What are "factors" in Mendelian explanations? American Breeders Association Reports, 5:365-369 (108,227 bytes; 4 pages, no figures)

Although T. H. Morgan is best known for heading the genetics laboratory at Columbia University (later at Cal Tech) that essentially defined American genetics research for decades, he was initially skeptical of the facile manner in which combinations of alleged Mendelian factors were being invoked to explain all manner of heritable traits.

This paper begins with a wonderful debunking of easy explanation:

In the modern interpretation of Mendelism, facts are being transformed into factors at a rapid rate. If one factor will not explain the facts, then two are invoked; if two prove insufficient, three will sometimes work out. The superior jugglery sometimes necessary to account for the result, may blind us, if taken too naïvely, to the common-place that the results are often so excellently "explained" because the explanation was invented to explain them. We work backwards from the facts to the factors, and then, presto! explain the facts by the very factors that we invented to account for them.

Bridges, Calvin B. 1914. Direct proof through non-disjunction that the sex-linked genes of Drosophila are borne on the X-chromosome. Science, NS vol. XL:107-109 (24,076 bytes; 5 pages, no figures)

Although Bridges' longer 1916 Genetics paper (vol 1, page 1) on the same topic is better known and treats the issue at much greater length, this short communication in Science contains the same argument and is equally persuasive.

By 1910, much evidence had been presented to demonstrate that sexual phenotype (i.e., maleness or femaleness) was determined by chromosomes. And, as early as 1902 Sutton noted that similarities in the behavior of genes and chromosomes suggested that Mendelian factors might be carried on chromosomes.

Here, Bridges shows that mis-assortment of the sex chromosomes is accompanied by atypical inheritance patterns for sex-linked traits and he argues that this proves that genes are carried on chromosomes. He concludes his paper: "there can be no doubt that the complete parallelism between the unique behavior of the chromosomes and the behavior of sex-linked genes and sex in this case means that the sex-linked genes are located in and borne by the X-chromosomes."

Muller, Herbert J. 1922. Variation due to change in the individual gene. The American Naturalist, 56:32-50. (126,062 bytes; 17 pages, no figures)

This paper is from an address given by to the thirty-ninth annual meeting of the American Society of Naturalists, held in Toronto on 29 December 29 1921.

In this remarkably prescient analysis, Muller lays out the paradoxical nature of the genetic material. It is apparently both autocatalytic (i.e., directs its own synthesis) and heterocatalytic (i.e., directs the sythesis of other molecules), yet only the heterocatalytic function seems subject to mutation. With this, he defines the key problems that must be solved for a successful chemical model of the gene.

Muller also anticipated the ultimate development of molecular genetics:

That two distinct kinds of substances -- the d'Hérelle substances (NOTE: viruses) and the genes -- should both possess this most remarkable property of heritable variation or "mutability," each working by a totally different mechanism, is quite conceivable, considering the complexity of protoplasm, yet it would seem a curious coincidence indeed. It would open up the possibility of two totally different kinds of life, working by different mechanisms. On the other hand, if these d'Hérelle bodies were really genes, fundamentally like our chromosome genes, they would give us an utterly new angle from which to attack the gene problem. They are filterable, to some extent isolable, can be handled in test tubes, and their properties, as shown by their effects on the bacteria, can then be studied after treatment. It would be very rash to call these bodies genes, and yet at present we must confess that there is no distinction known between the genes and them. Hence we cannot categorically deny that perhaps we may be able to grind genes in a mortar and cook them in a beaker after all. Must we geneticists become bacteriologists, physiological chemists and physicists, simultaneously with being zoologists and botanists? Let us hope so.

Riddle, Oscar. 1924. Any Hereditary Character and the Kinds of Things We Need to Know About It. The American Naturalist, LVIII:410-425. (80,148 bytes; 13 pages, no figures)

This does not qualify as a classic genetics paper and I suspect that it has never before been included in a collection of important papers. However, it is included here because it provides a glimpse into some general aspects of genetic thought in the mid 1920's.

The premise of this essay is essentially that, as of its writing, " studies on heredity and evolution offer what is mainly a two-sided attack on a many-sided problem." This argument was well taken, but the modern reader may have difficulty appreciating other concerns of the essay.

Wright, Sewall. 1932. Complementary Factors for Eye Color in Drosophila The American Naturalist, LXVI:282-283. (7,701 bytes; 2 pages, no figures)

There are two distinct biochemical pathways producing pigments that color the eyes of Drosophila melanogaster -- one yields a bright red pigment, the other brown. When both are present, the eyes are dark-red. When one is present and the other absent, flies have brown or bright red eyes. When both are missing, flies have white eyes.

In 1932, Sewall Wright reported the first case where a cross between red-eyed and brown-eyed flies yielded double-recessive progeny with white eyes. What makes this observation interesting is that the work occurred as part of a class exercise in an undergraduate teaching laboratory at the University of Chicago. Not many modern undergraduate lab exercises yield publishable results.