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passage 3
P1
In the eighteenth century the French naturalist Jean Baptiste de Lamarck believed that an animal's use or disuse of an organ affected that organ's development in the animal's offspring. ███
Intro to Topic ·
Lamarckianism
Environmentally induced adaptations can somehow be inherited.
Example ·
Giraffe's neck
Mama giraffe stretched its neck out to reach tall leaves (that's the environmentally induced adaptation). Somehow baby giraffe is able to inherit a long neck.
Problem with Lamarckianism ·
No genetic mechanism for inheritence
Biologists couldn't find genetic mechanism that could explain how baby giraffe could inherit mama giraffe's long neck.
New Evidence ·
of the phenomenon
Scientists newly discovered numerous examples. I'm expecting to read on to find examples of where a mama organism's environmentally induced adaptation gets passed onto her babies.
P2
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Example 1 ·
Bacteria pass on lack of walls
Environmentally induced adaptation in this case is the loss of cell walls in bacteria. This adaptation (loss of cell wall) does get passed onto subsequent generations of bacteria. The mechanism of inheritance is not via genes but rather via the interaction among genes.
P3
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Example 2 ·
Genes can be added or deleted
Example 2.1 ·
Fruit flies
Virus can infect fruit flies and add a gene which will get passed on. If infected flies are kept warm during reproduction, the virus is eliminated and so is the gene.
Example 2.2 ·
E. coli
If an E. coli bacterium with a certain kind of gene comes into contact with another without that kind of gene, the gene can be inserted into latter, which will then get passed onto its offspring.
Example 2.2 ·
Speculation
The causal mechanism found in E. coli could have helped to speed up evolution. For example, complex cells could have acquired photosynthesis by having come into contact with bacterium that possessed the photosynthesis gene.
P4
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Implications ·
Gene inheritance can be "vertical" or "horizontal"
"Vertical" inheritance is what we are familiar with, inheritance of genes from from ancestors. "Horizontal" inheritance is what the previous paragraphs described: from viruses, plasmids, bacteria, or other environmental agents.
Conclusion ·
Horizontal transmission may be the mechanism for inheritance that Lamarck needed
Passage Style
Phenomenon-hypothesis
Single position
18.
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a
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b
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c
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d
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e
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