PT79.S4.Q22 - after a hepadnavirus inserts itself

Comments

• Tinyosi1 Alum Member

  November 2016 235 karma

  My reasoning for believing that C would strengthen it is because if the insertion occurs at a random spot when a species initially receives it, and the two birds have it in the exact same spot, it strengthens the arguments that the virus was contracted 25 million years ago by an ancestor.
  
  Think about it: If the HV is always in the same spot, who cares if the birds have it in the exact same spot? Everyone would have it in the exact same spot. If it were in the same spot, the two birds could have got it at any time after diverging from their ancestor. This element of randomness makes that highly unlikely.
• 3 Likes

  stepharizona Alum Member

  November 2016 3197 karma

  @nantesorkestar said:
  I just can't see any assumptions the argument is making. In my opinion, C might weaken the argument if the insertion occurs at a random spot. Doesn't this contradict that the fragments are in the same location?
  

  I was thinking the same thing, as it needs to be a copy BUT this does in fact strengthen it, because if viruses inject themselves randomly the marker wouldnt be in the same spot in the two birds. I have a slightly different taken than @Tinyosil but as along the same lines if it is random it makes it unlikely that two birds would have it in the same spot, unless they have had it "copied" into their DNA at the same spot.
  
  We are told the species diverged 25 million years ago. If virus go into the DNA in a random spot, it is highly unlikely that the birds would have HV in the same spot in their DNA unless it was there before the divergence occurred. So because HV was there before the two species happened, it is present in the same place in their DNA.
• Seriousbird Alum Member

  November 2016 1278 karma

  @stepharizona I was also on that BR call last night and still confused, but your explanation to me explains everything!!
  
  Thank You!!!!
• nantesorkestar Alum Member

  November 2016 431 karma

  @stepharizona said:
  We are told the species diverged 25 million years ago. If virus go into the DNA in a random spot, it is highly unlikely that the birds would have HV in the same spot in their DNA unless it was there before the divergence occurred. So because HV was there before the two species happened, it is present in the same place in their DNA.
  

  Wow, thank you!
• stepharizona Alum Member

  November 2016 3197 karma

  @sweetsecret & @nantesorkestar This was a tricky one for sure... I too thought it was a weakener and had written "No has to be a copy"/same spot next to it... it wasn't till the call I realized this supported that it DID in fact mean that... Tricky LSAT...
• Madssssss L. Alum Member

  June 2019 124 karma

  And how would be disprove answer choice A?
• duncan chiu Alum Member

  May 2020 10 karma

  @"Madssssss L." said:
  And how would be disprove answer choice A?

  It took me a few reviews to finally see C as the correct AC, i chose A under timed. The reason why A is wrong is because the conclusion is that the virus is 25 million years old. Saying that viruses can affect the evolution of an organism is completely irrelevant to that conclusion. The premise isn't that the virus caused the divergence in species. Rather, it's that a ancestor of the 2 species existed 25 million years ago and that the hepadnavirus was within that ancestor's DNA/chromosomes. There are definitely other gaps in the argument but that's why A isn't stregnthening.