Six experimental DNA sequences labeled D1 through D6 are being studied

Question

Six experimental DNA sequences labeled D1 through D6 are being studied. Each sequence contains a unique combination of four-letter genetic codes made of the letters A, T, C, and G.

It is known that a “natural” group of DNA are all related by a mutation rule: each sequence mutates into the next by changing exactly one letter in the code and no sequence is repeated twice. However, one of the sequences being observed is a fake and does not belong in the “natural” group with the others.

Here are the DNA being observed:

- D1: ATCG
- D2: ATCA
- D3: TTCG
- D4: ATGG
- D5: ATTG
- D6: ATCC

Based on the mutation rule, select for Fake the sequence that does not belong in the “natural” group, and for 3rd the DNA sequence that is the third in a valid mutation chain.

Rohit_842 · Answer

Mutation sequence: d6 d2 d1 d4 d5. Invalid d3

GmatTest2026 · Answer

Solution:

By looking at the different sequences, the only sequence that works is D2->D6->D1->D4->D5. As it is said, the mutation rule: each sequence mutates into the next by changing precisely one letter in the code, and no sequence is repeated twice.

1. D2(ATCA)->D6(ATCC)-->4th position

2. D6(ATCC)-->D1(ATCG)-->4th position

3. D1(ATCG)-->D4(ATGG)-->3rd position

4. D4 (ATGG)-->D5(ATTG)-->3rd position

The only sequence that doesn't work is D3( TTCG)

So, D1 is the third position among the sequences, and D3 seems to be a Fake one.

agrotechpepper · Answer

Not clear on how to choose to choose the beginning of sequence. Kindly help

srik410 · Answer

You can start anywhere and start digging. Say I start with D1 my tree goes D1<->D6<->D2? D1<->D3? D1<->D4<->D5? D1<->D5<->D4? D1<->D2<->D6? Now, look for 5 length chain(because given 1 fake). Generally you can make those if you put 2 on one side of D1 and two on other side. So, in fact we have D6->D2-> D1 ->D5->D4 or D6->D2-> D1 ->D4->D5 or another 2 by swapping D2 and D6 at the start. In both these, you have D1 in the 3rd position and no D3 in the chain

agrotechpepper · Answer

Thanks for the clarification. But is this trial and error not going to take up a lot of time? I mean it took me close to 4 mins just to come up with your sequence given below. Am i doing something wrong?

cheshire · Answer

It shouldn't take that long as this isn't completely trial and error. You have to find combinations that sequence correctly and then work from there. Look for a few that mutate according to the rules and then try and make the others fit. If nothing is working, start with a different combination. This question is more of a puzzle than anything else.

Six experimental DNA sequences labeled D1 through D6 are being studied

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Two-part Analysis (TPA) Questions

Six experimental DNA sequences labeled D1 through D6 are being studied

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards