The nucleus of the cell is the organelle that is reponsible for heredity H ckel Boveri and specific kinds of cells the gametes that are separate and distinct from the rest of the body are responsible for generating progeny Weissman Inside the cell lie the chromosomes Flemming that separate into daughter cells via mitosis Proper development of an organism requires a specific set of a particular kind of chromosome Boveri 1 What is being omitted for lack of time MCB140 01 29 07 1 There is a striking concordance between the behavior of Mendel s particles and chromosomes during meiosis Sutton and Cannon 1902 3 2 1 H ckel Weissmann Flemming Boveri 1850 1900 3 Heredity operates via particles of information genes For any trait two particles alleles of a gene come together in an organism but then separate into gametes one per gamete This process occurs independently for particles genes for different traits Mendel 1853 66 1 2 MCB140 01 29 07 3 1 The rediscovery of Mendel s laws by Correns Tschermak and de Vries 2 The finding by Cuenot and by Castle that Mendel s laws also apply to mammals such as mice and guinea pigs 3 2 1 Genetics the narrative so far 2 1 William Bateson MCB140 01 29 07 4 MCB140 01 29 07 2 The genetic screen use of purposeful mutagenesis to identify genes required for the development of various traits Mapping by linkage and association mapping the study of simple and complex traits by analysis of pedigrees and populations Morgan and Bridges genes lie on chromosomes 1910 1915 Bateson and Sturtevant 1906 15 some genes appear to be physically linked the nature of this linkage is the following genes are arranged on a chromosome in a linear order at particular distances from each other McClintock and Stern 1930 genetic recombination occurs when homologous chromosomes can exchange parts Beadle and Tatum 1946 some genes affect the development of traits by encoding biochemical functions one gene one enzyme Muller 1927 the gene can be purposefully mutated Benzer the gene itself can be split into smaller units Studying the molecular makeup of life via he privately subsidized his small book Mendel s Principles of Heredity A Defence and he sent copies to all of the leading students of heredity to make sure that Mendel would not suffer another 35 years of neglect Carlson Mendel s Legacy 5 6 7 4 3 1 2 Genetics the narrative to come 1 Bateson 1902 Modified Mendelian ratios epistasis MCB140 01 29 07 7 MCB140 01 29 07 5 Bateson 1902 each other MCB140 01 29 07 8 MCB140 01 29 07 6 Repulsion and coupling linkage 2 Fig 3 7 Sturtevant Bridges Muller Morgan MCB140 01 29 07 9 Genes lie on chromosomes Emphasis mine fdu MCB140 01 29 07 12 As will be shown now certain factors follow the distribution of the X chromosome and are therefore supposed to be contained in them Morgan et al 1915 MCB140 01 29 07 10 Thomas Hunt Morgan the first nativeborn American to win the Nobel Prize founder of modern genetics 3 MCB140 01 29 07 15 The value and utility of any experiment Mendel What was needed to open up genetics to new phenomena was an organism that bred rapidly produced lots of progeny and was inexpensive to maintain Carlson Fruit flies can be raised on a mixture of corn meal yeast sugar and agar Flies complete their life cycle from fertilization to emergence of the adult fly in 10 days A female can produce 3 000 progeny in her lifetime A single male can sire well over 10 000 offspring Hartwell A problem and a solution MCB140 01 29 07 13 Bateson W 1916 The mechanism of Mendelian heredity a review Science 44 536 543 The supposition that particles of chromatin indistinguishable from each other and indeed almost homogeneous under any known test can by their material nature confer all the properties of life surpasses the range of even the most convinced materialism aka chr 1 Note no crossing over in male meiosis MCB140 01 29 07 16 MCB140 01 29 07 14 4 Morgan had been working on fruit flies for at least two years before he found his most significant mutation a white eyed fly For this new approach Morgan was his own first student He bred the fliles for two years without assistance He pointed to the shelves with flies and said that he had wasted two years and had gotten nothing for his work Tough early going MCB140 01 29 07 19 MCB140 01 29 07 20 May 1910 was when the revolution began Morgan found a white eyed male running around in one bottle MCB140 01 29 07 18 Morgan was not a geneticist by training he was an embryologist and he was not the first one to use Drosophila for purposes of genetic research Castle was One of the baffling problems of breeders in pre Mendelian days had been the effects of inbreeding and crossbreeding What these were was a much debated question We set out to give it an experimental test and found ready to hand a rapidly breeding little fly Drosophila being cultured in the laboratory by a graduate student as embryological material This he told us would complete a generation within a fortnight Charles Woodworth prof entomology at UC Berkeley We began culturing the fly on pulped Concord grapes but this gave us poor results as many of the larvae would get drowned and then our population statistics were no good As grapes became out of season we tried other fruits and finally hit the jackpot in bananas The conclusion drawn from our studies was that inbreeding reduces very slightly the productiveness of Drosophila This was not a conclusion of worldshaking importance The important outcome of this investigation was that it called to Morgan s attention a new source of material for experimental study not subject to the limitations of slow breeding laboratory mammals WE Castle prof genetics UC Berkeley The Beginnings of Mendelism in America in Genetics in the 20th Century p 73 Morgan and Drosophila go Bears 5 MCB140 01 29 07 21 MCB140 01 29 07 23 1 The paper itself 2 The commentary to it written by Robert Robbins that precedes the paper itself in the ESP generated PDF 3 Morgan s own description in narrative form pp 15 20 of his 1915 book also an ESP provided PDF Required reading for Morgan s Science paper When Caroline Meeber boarded the afternoon train for Chicago her total outfit consisted of a small trunk a cheap imitation alligator skin satchel a small lunch in a paper box and a yellow leather snap purse containing her ticket a scrap of paper with her sister s address in Van Buren Street and 4 dollars in money It was in August 1998 She was eighteen years of age bright timid and full of the
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