How To Draw A Polygenteic Tree With Table

Do they just look for similarities between the whole genomes? Or just specific genes? Or RNA? Or what exactly?

- A high school student from Egypt

June 4, 2022

A phylogenetic tree is a diagram used to show how organisms are related to one some other.

There are actually a lot of different ways to make these trees! As long every bit y'all have something y'all can compare across different species, y'all can brand a phylogenetic tree.

A phylogenetic tree can be built using physical data like torso shape, os structure, or behavior. Or it can be built from molecular data, like genetic sequences.

In general, the more information you're able to compare, the more accurate the tree will exist. So you'd get a more authentic tree by comparing unabridged skeletons, instead of merely a single bone. Or by comparison entire genomes, instead of simply a unmarried gene.

Any DNA, RNA, or protein sequence tin can be used to generate a phylogenetic tree. Only Dna sequences are most commonly used in generating trees today.

What's in a phylogenetic tree?

In a phylogenetic tree, each line is called a co-operative. The end of each branch is chosen a tip– this is where you put a species!

Each point where the two branches dissever is chosen a node. A node is the most recent common ancestor of all species on those branches.

And if yous go all the manner down to the bottom of the tree, the last node is called the root. This is the common ancestor all the species in the tree!

You can depict phylogenetic trees in many dissimilar shapes. Information technology doesn't thing whether it's rectangular or circular. The import function is how it is branched. The branching represents the differences in the relationship of species.

These trees all show exactly the same information! Just in different shapes.

How to construct a phylogenetic tree?

Any Deoxyribonucleic acid, RNA, or protein sequences can be used to describe a phylogenetic tree. Only DNA sequences are the most widely used. It'southward pretty cheap and easy at present to get DNA sequences. Plus Deoxyribonucleic acid contains more data, which can brand more accurate trees. For example, some changes in Deoxyribonucleic acid sequences do non pb to changes in proteins.

To construct a tree, we'll compare the Dna sequences of unlike species.

Evolutionarily related species have a mutual ancestor. Before they split into dissever species, they had exactly the aforementioned Deoxyribonucleic acid. Only as species evolve and diverge, they volition accumulate changes in the Dna sequences.

Nosotros tin can utilize these changes in the Dna to tell how closely related ii species are. If there aren't very many differences, they're probably closely related. If there are a lot of changes, they might be more distant relatives.

The offset matter to do is align the ii DNA sequences together that y'all're going to compare. Make sure you're comparison the same gene! (Or other sequence.) Otherwise you lot are comparing apples to oranges.

This sequence alignment is frequently washed with the assist of figurer programs. The strategy is to find the alignment that has the most matches and the to the lowest degree mismatches.

You can marshal and compare as many sequences as yous want. Remember, the more information you consider, the more accurate your tree will be!

Convert sequence alignment to a relatedness

Ok, and so you've got your Deoxyribonucleic acid aligned. Now what? How do you catechumen that into a tree?

Next you compare the sequences, to encounter how similar they are to each other.

We can see that Sequence #1 vs #2 have one difference. Sequence #two vs #3 have 2 differences. Sequences #3 vs #four has five differences. And then on.

Just by looking at them, we can see that Sequences 1 and 2 are pretty similar. We would grouping them together in a tree.

But we can do better than simply looking at them. You tin can really summate how like any two sequences are, and make a table to compare all the differences. This especially helps when you're comparing a lot of information!

Sequences 1 and two differ by 1 nucleotide, out of the 20 full. Then the difference between Sequence 1 and 2 is:

1/20= 0.05

Nosotros tin calculate the deviation between each pair of sequences. If we put the calculated differences in a matrix, it would expect like this:

Now if you await at the matrix, the pairs that take the everyman values are the most similar. As before, nosotros can see that sequences ane and two are very similar. So we can put ane and ii together.

After we put one and ii together, we will have to recalculate the difference between sequences. At present that we've i-2 together in the tree, we're going to consider them every bit a single group. We'll calculate the differences with other sequences by taking an average.

For example, the deviation between 1&2 vs three would exist:

Average of (1 vs 3) and (2 vs 3) = one-2 vs iii
½ * (0.1+0.ane)= 0.1

Similarly, we could calculate the differences with other sequences. We would take a table like beneath:

Looking at the table, we can see 3 is about similar with 1-ii. And so we can group 3 together with one-ii.

Now, we will repeat the to a higher place steps. We will treat 1, 2, and iii as one species equally nosotros proceed edifice the tree. We'll use the boilerplate of 1-two vs other and iii vs otherto do this.

For example, the divergence betwixt 1-3 and four would be:

Average of (1-2 vs iv) and (iii vs 4) = i-ii-iii vs four
½ * (0.two+0.25) = 0.225

Nosotros can calculate the rest with the same method. Now we have a table as below:

We tin can see that 1-3 and 4 are virtually like. So we can put 4 and ane-3 together.

Now we can add in sequence 5 and get our tree!

You tin apply this method to build all sorts of copse! Not all trees volition look like this one, merely the aforementioned basic principles will utilise.

By Allison Zhang, Stanford University

Source: https://genetics.thetech.org/ask-a-geneticist/how-build-phylogenetic-tree

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