Thomas Hunt Morgan the first nativeborn American to win the Nobel Prize founder of modern genetics Enter the fruit fly MCB140 9 8 08 1 MCB140 9 8 08 2 Morgan et al 1915 Bridges As will be shown now certain factors follow the distribution of the X chromosome and are therefore supposed to be contained in them Morgan Muller Emphasis mine fdu Genes lie on chromosomes Sturtevant MCB140 9 8 08 4 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 5 MCB140 9 8 08 6 1 A problem and a solution aka chr 1 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 Note no crossing over in male meiosis MCB140 9 8 08 7 MCB140 9 8 08 8 Morgan 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 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 MCB140 9 8 08 10 May 1910 was when the revolution began Morgan found a white eyed male running around in one bottle Tough 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 11 MCB140 9 8 08 12 2 One 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 13 MCB140 9 8 08 14 MCB140 9 8 08 15 MCB140 9 8 08 16 The Mechanism of Mendelian Heredity 1915 Thomas Hunt Morgan Alfred Sturtevant Hermann Muller Calvin Bridges Nothing special here Just like seed color in peas Normal Mendelian ratio 3 1 but where are the white eyed females MCB140 9 8 08 17 MCB140 9 8 08 18 3 MCB140 9 8 08 19 Nettie Stevens discoverer of the sex chromosomes Nettie 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 for a research position She was eventually given an assistantship by the Carnegie Institute after glowing recommendations from Thomas Hunt Morgan Edmund Wilson and M Carey Thomas the president of Bryn Mawr Her work on sex determination was published as a Carnegie Institute report in 1905 MCB140 9 8 08 20 The useful mealworm It is perfectly clear that an egg fertilized by a spermatozoon containing the smaller hererochromosome produces a male while one fertilized by a spermatozoon containing the larger heterochromosome develops into a female XO is male and XX is female until 1916 MCB140 9 8 08 21 Edmund Wilson arguably the first XY person on Earth MCB140 9 8 08 22 Dr Thomas Ried NCI NIH SKY of hormal human cell In many species of insects there are two classes of spermatozoa equal in number which in the early stages of their development differe visibly in respect to the nuclear constitution while there is but one class of egg That is to say if the two kinds of spermatozoa be designated as the X class and the Yclass respectively the eggs are all of the X class The male may accordingly be designated as the heterogametic sex the female as the homogametic MCB140 9 8 08 23 MCB140 9 8 08 24 4 MCB140 9 8 08 25 MCB140 9 8 08 26 MCB140 9 8 08 27 MCB140 9 8 08 28 MCB140 9 8 08 29 MCB140 9 8 08 30 5 Calvin Bridges MCB140 9 8 08 31 raised by his grandparents in upstate New York both of his parents dying
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