Self-study
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 (RC)
Single position
13.
The passage suggests that many ██████████ ██ ██████ ███████ █████ ███ ██ ███ ██████████
a
An organ's use ██ ██████ ███ ██████ ████ ███████ ████████████
This describes Lamarck’s belief – but this is not a belief that many biologists used to hold. We’re only told that Lamarck believed this; we don’t know whether others agreed with him but then changed their minds. If anything, now that there’s new research about the potential for inheritance of acquired characteristics, (A) describes a belief that many biologists did not used to hold, but are now more open to.
b
Some but not ███ █████ ███ █████████ █████████████
This isn’t a belief that many biologists used to hold, but no longer hold. In fact, now that there’s new research about the potential for inheritance of acquired characteristics, (B) describes a belief that many biologists did not used to hold, but are now more open to.
c
All genes are █████████ █████████████
This isn’t a belief that many biologists used to hold. In fact, many biologists used to hold that all genes are inherited vertically (meaning, from their ancestors).
d
Some but not ███ █████ ███ █████████ ███████████
This isn’t a belief that many biologists used to hold, but no longer hold. In fact, many biologists used to hold that all genes are inherited vertically (meaning, from their ancestors).
e
All genes are █████████ ███████████
This is supported by the fact that new research shows the long-held belief that inheritance of acquired characteristics never occurs is actually mistaken. Previously, biologists thought genes could only be inherited from ancestors (vertical inheritance, as described in the last paragraph). But now the passage suggests that there are biologists who are open to horizontal inheritance (inheritance from viruses, plasmids, bacteria, or other environmental agents). If you have a problem with the fact the passage never explicitly says that many biologists have changed their long-held belief against horizontal inheritance, remember that this is not a Must Be True question in LR. This is an Implied question in RC. The standard for support is lower. And what else can you pick? There’s no other answer that has any amount of support. Get used to picking the best of 5 answers, even if you don’t think it’s perfect.