04 - Chromosome "theory" of inheritance MCB140...

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MCB140 01-30-08 1 Chromosome “theory” of inheritance
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MCB140 01-30-08 2 Other “theories” Darwin’s “theory” of evolution Crick’s central “dogma” of molecular biology (information goes from DNA to protein and not the other way around) Galileo’s “theory” that the Earth rotates around its axis, and revolves around the Sun
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MCB140 01-30-08 3 Mendel’s “Particles of Inheritance” (the Genes) Lie on Chromosomes: From Theory in the 1900s to Firmly Established Fact by ~1920
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MCB140 01-30-08 4 Ernest Häckel 1866: General Morphology of the Organisms “The nucleus is the part of the cell that is responsible for heredity” Nice idea, but not based on data of any sort (at the time).
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MCB140 01-30-08 5 August Weissman, 1883
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MCB140 01-30-08 6 Recall Darwin’s “gemmules”… soma Germ plasm soma Germ plasm
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MCB140 01-30-08 7 Weissman’s somewhat gruesome but, well, persuasive experiment 1. Cut off the tail of some mice. 2. Breed the tailless mice. 3. Get children with tails. 4. Cut off their tails. 5. Breed them. Repeat 21 times. “Experiments” done by others and cited by Weissman as supporting evidence: centuries and centuries of foot-binding by the Chinese and circumcision by the Jews have not led to the inheritance of either trait.
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MCB140 01-30-08 8
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MCB140 01-30-08 9 Walther Flemming, 1879 Salamander tail fin cells – living cells. Gills – fixed cells. “Beitrage zur kentniss der Zelle und ihre Lebenserscheinungen “Contributions to knowledge about the cell and of aspects of its appearance that have to do with the fact that it is alive .”
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a process with threads = mitosis
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MCB140 01-30-08 11 The object that acquires a color after we stain it: the chromosome Flemming stained the cell with a dye and found that something inside the nucleus stained quite vigorously. He called it “chromatin” (“stainable material”). In 1888, Waldeyer renamed Flemming’s “threads” – “chromosomes.”
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MCB140 01-30-08 12 A question What – if anything – do the chromosomes have to do with the process of heredity?
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MCB140 01-30-08 13 Theodor Boveri, 1895
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MCB140 01-30-08 14 Boveri, expt 1 1. Enucleate sea urchin egg by agitation. 2. Fertilize this “cytoplasm only” egg with sperm. 3. To his surprise, get a larva, but a much smaller one. “… It is not a given number of chromosomes as such that is required for normal development, in as much as these fragments, although they contained only half the normal amount of chromatin and half the number of elements, namely the chromosomes of one sperm nucleus, still give rise to normal plutei.” Pluteus = easel.
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MCB140 01-30-08 15
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MCB140 01-30-08 16 Boveri, expt. 2 Enucleate the egg of one species of sea urchin, and fertilize with a sperm of a different species.
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MCB140 01-30-08 17
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MCB140 01-30-08 18
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MCB140 01-30-08 19 E.B. Wilson, 1896 “… the maternal cytoplasm has no determining effect on the offspring, but supplies only the material in which the sperm nucleus operates. Inheritance is, therefore, affected by the nucleus alone.”
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This note was uploaded on 08/01/2008 for the course MCB 140 taught by Professor Urnov during the Spring '08 term at University of California, Berkeley.

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04 - Chromosome "theory" of inheritance MCB140...

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