In vertical inheritance, parents pass genes to their offspring, but in horizontal transfer (HT), one species, often bacteria, passes genetic...
GMAT Information and Ideas : (Ideas) Questions
In vertical inheritance, parents pass genes to their offspring, but in horizontal transfer (HT), one species, often bacteria, passes genetic material to an unrelated species. In a 2022 study, herpetologist Atsushi Kurabayashi and his team investigated HT in multicellular organisms—namely, snakes and frogs in Madagascar. The team detected BovB—a gene transmitted vertically in snakes—in many frog species. The apparent direction of gene transfer seems counterintuitive because frogs usually don't survive encounters with snakes and so wouldn't be able to transmit the newly acquired gene to offspring, but the team concluded that BovB is indeed transmitted from snakes to frogs, either directly or indirectly, via HT.
Which finding, if true, would most directly support the team's conclusion?
BovB can be transmitted across frog species through HT.
Parasites known to feed on species of snakes and frogs in which the BovB gene occurs also carry BovB.
BovB cannot be reliably transmitted from a snake species to bacteria that are usually encountered by frog species.
Frog species with BovB show few discernible advantages as compared with frog species that do not carry BovB.
Step 1: Decode and Map the Passage
Part A: Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| 'In vertical inheritance, parents pass genes to their offspring, but in horizontal transfer (HT), one species, often bacteria, passes genetic material to an unrelated species.' |
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| 'In a 2022 study, herpetologist Atsushi Kurabayashi and his team investigated HT in multicellular organisms—namely, snakes and frogs in Madagascar.' |
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| 'The team detected BovB—a gene transmitted vertically in snakes—in many frog species.' |
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| 'The apparent direction of gene transfer seems counterintuitive because frogs usually don't survive encounters with snakes and so wouldn't be able to transmit the newly acquired gene to offspring,' |
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| 'but the team concluded that BovB is indeed transmitted from snakes to frogs, either directly or indirectly, via HT.' |
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Main Point: Researchers concluded that a snake gene found in frogs represents horizontal gene transfer from snakes to frogs, despite the apparent problem that frogs typically don't survive snake encounters.
Step 2: Interpret the Question Precisely
What's being asked? Which finding would most directly support the team's conclusion that BovB is transmitted from snakes to frogs via horizontal transfer.
What type of answer do we need? Evidence that would strengthen or support their conclusion about the mechanism of transfer.
Any limiting keywords? 'most directly support' - needs the strongest, most relevant evidence.
Step 3: Prethink the Answer
- The team's conclusion is that BovB transfers from snakes to frogs via horizontal transfer, but they acknowledged this seems counterintuitive because frogs don't survive snake encounters
- So we need evidence that explains HOW this transfer could actually happen despite that problem
- The right answer should provide a plausible mechanism or pathway that would allow the snake gene to reach frogs without requiring direct snake-frog contact that the frogs survive
BovB can be transmitted across frog species through HT.
- This tells us HT can happen between different frog species, but it doesn't explain how BovB got from snakes into frogs in the first place
Parasites known to feed on species of snakes and frogs in which the BovB gene occurs also carry BovB.
- This provides a mechanism—parasites that feed on both snakes and frogs also carry BovB
- This explains exactly how the gene could transfer indirectly: snake → parasite → frog
BovB cannot be reliably transmitted from a snake species to bacteria that are usually encountered by frog species.
- This says the gene can't transfer from snakes to bacteria that frogs encounter
- This actually weakens the conclusion by eliminating a potential transfer mechanism
Frog species with BovB show few discernible advantages as compared with frog species that do not carry BovB.
- This is about whether BovB gives frogs advantages
- The presence or absence of advantages doesn't explain how the transfer occurred