Enter the fruit flyThomas Hunt Morgan, the first native-born American to win the Nobel Prize, founder of modern geneticsSlide 3Morgan et al. 1915Slide 5Slide 6A problem and a solutionSlide 8Slide 9Morgan and Drosophila (go Bears)Tough early going“May 1910 was when the revolution began. Morgan found a white-eyed male running around in one bottle.”One of the best-known opening passages in the history of the English languageSlide 14“The Mechanism of Mendelian Heredity” (1915)Slide 16Slide 17Slide 18Slide 19Slide 20Nettie Stevens, discoverer of the sex chromosomesThe useful mealwormEdmund Wilson – arguably, the first XY person on EarthSlide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Calvin BridgesvermilionSlide 34Criss-cross inheritance: white-eyed sons and red-eyed daughters of white-eyed mothers and red-eyed fathersThe “exceptional female” appearsSlide 37Slide 38Slide 39How could a white-eyed mother have a white-eyed daughter?Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Bridges, C. B. 1935. Salivary chromosome maps with a key to the banding of the chromosomes of Drosophila melanogaster. J. Hered. 26: 60–64Slide 49Fine, fine, genes are on chromosomes. Now what?MCB140 9-8-08 1Enter the fruit flyMCB140 9-8-08 2Thomas Hunt Morgan, the first native-born American to win the Nobel Prize, founder of modern geneticsBridgesMullerMorganSturtevantMCB140 9-8-08 4Morgan et al. 1915“As will be shown now, certain factors follow the distribution of the X chromosome and are therefore supposed to be contained in them.”Emphasis mine – fdu. ↓Genes lie on chromosomesMCB140 9-8-08 5“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.” Bateson, W. (1916) The mechanism of Mendelian heredity (a review). Science, 44, 536-543.MCB140 9-8-08 6MCB140 9-8-08 7A problem and a solution“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)MCB140 9-8-08 8(aka chr. 1)Note: no crossing over in male meiosis!MCB140 9-8-08 10Morgan and Drosophila(go Bears)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 world-shaking 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.MCB140 9-8-08 11Tough early going“… 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.”MCB140 9-8-08 12“May 1910 was when the revolution began. Morgan found a white-eyed male running around in one bottle.”MCB140 9-8-08 13One of the best-known opening passages in the history of the English language“It is a truth universally acknowledged that a single man in possession of a good fortune must be in want of a wife.”MCB140 9-8-08 14MCB140 9-8-08 15“The Mechanism of Mendelian Heredity” (1915)Thomas Hunt MorganAlfred SturtevantHermann MullerCalvin BridgesMCB140 9-8-08 16MCB140 9-8-08 17MCB140 9-8-08 18Nothing special here.Just like seed color in peas.Normal Mendelian ratio (3:1) – but where are the white-eyed females?!!MCB140 9-8-08 19MCB140 9-8-08 20MCB140 9-8-08 21Nettie Stevens, discoverer of the sex chromosomesNettie Stevens was one of the first female scientists to make a name for herself in the biological sciences. She was born in Cavendish, Vermont. Her family settled in Westford, Vermont. Stevens' father was a carpenter and handyman. He did well enough to own quite a bit of Westford property, and could afford to send his children to school.Stevens was a brilliant student, consistently scoring the highest in her classes. In 1896, Stevens went to California to attend Leland Stanford University. She graduated with a masters in biology. Her thesis involved a lot of microscopic work and precise, careful detailing of new species of marine life. This training was a factor in her success with later investigations of chromosomal behavior.After Stanford, Stevens went to Bryn Mawr College for more graduate work. Thomas Hunt Morgan was still teaching at Bryn Mawr, and was one of her professors. Stevens again did so well that she was awarded a fellowship to study abroad. She traveled to Europe and spent time in Theodor Boveri's lab at the Zoological Institute at Wurzburg, Germany. Boveri was working on the problem of the role of chromosomes in heredity. Stevens likely developed an interest in the subject from her stay.In 1903, Stevens got her Ph.D. from Bryn Mawr, and started looking
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