using the data that shows the number of dna sequence difference among 6 organisms, create a phylogenetic tree

Question

Org/Org Org1 Org2 Org 3 Org4 Org5 org 6

Org1 0 4 1 2 3 3

Org2 0 3 6 7 1

Org3 0 3 4 2

Org4 0 1 5

Org5 0 6

Please show me what is the group and how the tree was drawn based on the data

Answer 1

Hi Vina,

This is an interesting question. There are a few differnt ways to go about this, and in the real world we would probably let a computer program figure it out for us.

As I was researching how best to help you, I found this explanation at Khan Academy:

https://www.khanacademy.org/science/ap-biology/natural-selection/phylogeny/a/building-an-evolutionary-tree

And Sal from Khan Academy does a great job of building a tree using the template provided in this video:

https://www.khanacademy.org/science/ap-biology/worked-examples-ap-biology/worked-examples-2015/v/2015-ap-biology-free-response-3

Those two resources are great for understanding how this all works. Now on to your question. In a step-by-step process:

1. I first rewrote the data you gave us into a spread sheet table. Because I am a very visual person, I used different colors to identify the degrees of difference.
2. But I was still having trouble seeing the relationships. So I regrouped the organisms into a table based on the number of differences they had in relation to the other organisms. It looked like this:
3. Org1 & Org 3, Org5 & Org4, Org2 & Org6
4. Org1 & Org4, Org3 & Org6
5. Org3 & Org2, Org3 & Org4, Org1 & Org5, Org1 & Org6
6. Org1 & Org2, Org5 & Org3
7. Org4 & Org 6
8. Org2 & Org4, Org5 & Org 6
9. Org5 & Org 2
10. You did not provide a template, so I still needed a visual for the actual tree. Still in the psreadsheet, I started putting organisms in cells, starting with Org5 and Org2 seven cells apart in a step formation (on a 6 by 7 grid).
11. Then I put the next closest organisms into the grid. Org5 and Org4 are one step apart, as are Org 2 and Org6.
12. That left me Org1 and Org3 and multiple relationships. So I stuck them together in the middle of my table.

* * * * * * Org2

* * * * * Org6 *

* * * Org1 & Org3 * * *

* * * * * * *

* Org4 * * * * *

Org5 * * * * * *

1. Still with me? Since I had two organisms together in one cell, that made me think that I had a split branch in the tree, so I drew a template for myself and when I labeled my branches, I got this tree:

Org2

Org6 /

|_/

Org1 Org3 /

\ / /

\ / /

\/ /

| /

|_/

Org4 /

|_/

Org5 /

|_/

There is more than one answer to this question, but the one I have shown you here can be defended with the data given.