Gregor Mendel Versuche über Pflanzenhybriden“The offspring of hybrids in which several differing traits are associated”Slide 3Slide 4Slide 5Slide 6Ta-daaa! The second lawGasp #2Gasp #2 continuedGregor Mendel to Carl Nägeli, Dec. 31, 1866Slide 11ApomixisSlide 13Charles Darwin (1859) The Origin of Species by Means of Natural SelectionThe problem with step 2Sergei Chetverikov (1926) On certain aspects of the evolutionary process from the standpoint of modern geneticsArchibald Garrod (1902)Ah!Slide 19Chromosome “theory” of inheritanceOther “theories”Mendel’s “Particles of Inheritance” (the Genes) Lie on Chromosomes:Ernest HäckelSlide 24Slide 25Weissman’s somewhat gruesome but, well, persuasive experimentSlide 27Walther Flemming, 1879Slide 29The object that acquires a color after we stain it: the chromosomeA questionTheodor Boveri, 1895Boveri, expt 1Slide 34Boveri, expt. 2Slide 36Slide 37E.B. Wilson, 1896Boveri, expt. 3Boveri expt. 3 ctd.Next timeTo the benchMCB140 31-08-07 1Gregor MendelVersuche über PflanzenhybridenThe Second LawMCB140 31-08-07 2“The offspring of hybrids in which several differing traits are associated”“In the experiments above described plants were used which differed only on one essential character. The next task consisted in ascertaining whether the law of development discovered in these applied to each pair of differentiating characters when several diverse characters are united in the hybrid by crossing.” dihybrid crossMCB140 31-08-07 3“Two experiments were made with a considerable number of plants. In the first experiment the parental plants differed in the form of the seed and in the color of the albumen; in the second in the form of the seed, in the color of the albumen, and in the color of the seed-coats. Experiments with seed characters give the result in the simplest and most certain way.In order to facilitate study of the data in these experiments, the different characters of the seed plant will be indicated by A, B, C, those of the pollen plant by a, b, c, and the hybrid forms of the characters by Aa, Bb, and Cc.”MCB140 31-08-07 4MCB140 31-08-07 5MCB140 31-08-07 6MCB140 31-08-07 7Ta-daaa! The second law“There is therefore no doubt that for all of the traits involved in the experiments this statement is valid: the offspring of the hybrids in which several essentially different characters are combined exhibit the terms of a series of combinations, in which the developmental series for each pair of differentiating traits are combined. It is demonstrated at the same time that the relation of each pair of different traits in hybrid union is independent of the other differences in the two parental plants.”“Es unterliegt daher keinem Zweifel, dass für sämmtliche in die Versuche aufgenommenen Merkmale der Satz Giltigkeit habe: die Nachkommen der Hybriden, in welchen mehrere wesentlich verschiedene Merkmale vereinigt sind, stellen die Glieder einer Combinationsreihe vor, in welchen die Entwicklungsreihen für je zwei differirende Merkmale verbunden sind. Damit ist zugleich erwiesen, dass das Verhalten je zweier differirender Merkmale in Hybrider Verbindung unabhängig ist von den anderweitigen Unterschieden an den beiden Stammpflanzen.”MCB140 31-08-07 8Gasp #2“Even the validity of the law formulated for Pisum requires still to be confirmed, and a repetition of the more important experiments is therefore desirable … In the meantime we may assume that no basic difference could exist in important matters, since unity in the developmental plan of organic life is beyond question.”MCB140 31-08-07 9Gasp #2 continued“Indessen dürfte man vermuthen, dass in wichtigen Puncten eine principielle Verschiedenheit nicht vorkommen könne, da die Einheit im Entwicklungsplane des organischen Lebens ausser Frage steht.”This statement brings and “prescient” to new shades of meaning. Mendel – a peasant’s son who failed to graduate from college, and who worked alone in a monastery – says here that he believes to have discovered a general law of life, because he thinks that the same core principles underlie the functioning of all living beings.MCB140 31-08-07 10Gregor Mendel to Carl Nägeli, Dec. 31, 1866“Highly esteemed Sir:The acknowledged preeminence your Honor enjoys in the detection and classification of wild-growing plant hybrids makes it my agreeable duty to submit for your kind consideration the description of some experiments in artificial fertilization.”MCB140 31-08-07 11Gregor Mendel to Carl Nägeli, Dec. 31, 1866“I am not surprised to hear your honor speak of my experiments with mistrustful caution. … I knew that the results I obtained were not easily compatible with our contemporary scientific knowledge, and that under the circumstances publication of one such isolated experiment was doubly dangerous; dangerous for the experimenter and for the cause he represented. Thus I made every effort to verity, with other plants, the results obtained with Pisum.”MCB140 31-08-07 12Apomixis“In botany, apomixis is asexual reproduction, without fertilization and modified meiosis.The modified meiosis yields seeds that are genetically identical to the one of the parental plants.”In zoology, the cognate phenomenon is known as parthenogenesis.MCB140 31-08-07 13MCB140 31-08-07 14Charles Darwin (1859)The Origin of Species by Means of Natural Selection1. Living organisms multiply; resources are limited.2. Organisms vary. Some variation affects survival and reproduction.3. Like begets like.4. Populations of organisms will evolve: those organisms with characteristics most favourable for survival and reproduction will not only have more offspring, but will pass their characteristics onto those offspring. the characteristics seen in the population will changeheritable change in animals selection by environment adaptation to environmentMCB140 31-08-07 15The problem with step 2 “What was missing from Darwin’s theory was a source for the variations on which natural selection acted. … Darwin addressed the problem of heredity. He believed that smalled units, which he called gemmules, were produced by the cells, and them migrated through the body, and some of them would be retained in the … gonads.” EA Carlson, Mendel’s Legacy“The most unfortunate of the assumptions underlying Darwin’s mechanism of evolution was that of blending heredity; i.e., that parental differences are merged in the
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