Solved Phylogenetic trees worksheet 1. Consider the | Chegg.com - Free Printable

Let’s work through each part of the question step by step.

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Part a: Would a group composed only of fungi and Fonticula be monophyletic? Justify your answer.

First, what does “monophyletic” mean?
→ A monophyletic group (also called a clade) includes an ancestor and ALL of its descendants — nothing more, nothing less.

Now, look at the tree:

- Fungi and Fonticula are both under node 8.
- But node 8 also includes Nuclearia as a descendant.
- So if we take *only* Fungi and Fonticula, we’re leaving out Nuclearia — which is also a descendant of node 8.
→ That means this group is NOT monophyletic — it’s missing a descendant (Nuclearia).

Also, note that Fungi and Fonticula do NOT share a unique common ancestor that doesn’t include other groups — their most recent common ancestor (node 8) also gave rise to Nuclearia.

✔ So, no — it’s not monophyletic.

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Part b: Identify a monophyletic group of your choice that includes choanoflagellates. List all the members of this group and the node of the common ancestor.

Choanoflagellates are shown on the tree. Let’s find their position.

Looking at the tree:

- Choanoflagellates branch off after node 10.
- Node 10 is the common ancestor of Choanoflagellates, Sponges, Insects, Vertebrates, etc. — basically everything above node 10.
- But wait — let’s check: What’s the smallest monophyletic group that includes choanoflagellates?

Actually, choanoflagellates are sister to the group containing Sponges, Insects, Vertebrates, etc. — meaning they share a common ancestor at node 10 with all those animals.

So one valid monophyletic group including choanoflagellates is:

→ All descendants of node 10: Choanoflagellates, Sponges, Insects, Vertebrates.

But wait — is there a smaller group? No, because choanoflagellates don’t share a more recent exclusive common ancestor with any subset — they’re the first branch after node 10.

Alternatively, you could pick a larger group — like Opisthokonts (which includes fungi, animals, choanoflagellates, etc.), anchored at node 6 or 7.

But the question says “of your choice”, so let’s pick the smallest clear one.

Actually, looking again: Choanoflagellates are directly connected to node 10, and node 10 leads to:

- Choanoflagellates
- Then the rest: Sponges, then Insects/Vertebrates

So yes — the monophyletic group starting at node 10 includes:

Members: Choanoflagellates, Sponges, Insects, Vertebrates
Common ancestor node: 10

Wait — but actually, node 10 is the point where the lineage splits into Choanoflagellates and the animal line. So technically, node 10 is the common ancestor of Choanoflagellates AND the animals.

So yes — that’s correct.

Another option: You could include Capsaspora too — since Capsaspora branches off before node 10? Wait no — Capsaspora branches off at node 7, which is earlier.

Actually, let’s trace carefully:

From root up:

- Node 6 → leads to two branches: one to Breviatea, one to node 7.
- Node 7 → leads to Capsaspora and node 8.
- Node 8 → leads to Fungi, Fonticula, Nuclearia.
- Then node 10 comes after node 7? Wait — no, looking at the tree structure:

Actually, the tree shows:

After node 6, one branch goes to Breviatea, the other goes to node 7.

Node 7 has a trait “Single flagellum, Insertion in EF1a gene” and leads to:

- One branch to Capsaspora
- Another branch to node 8 (Fungi, Fonticula, Nuclearia)
- AND another branch to node 10? Wait — no, looking again:

Actually, from node 7, it seems to split into:

- Capsaspora
- And then a branch that goes to node 8 AND node 10? That doesn’t make sense.

Wait — let me re-read the tree layout.

Actually, the tree is drawn such that:

From node 6:

→ Left branch: Breviatea
→ Right branch: goes to node 7

From node 7:

→ One branch: Capsaspora
→ Another branch: goes to node 8
→ Another branch: goes to node 10? No — actually, looking at the diagram, node 7 leads to a branch that then splits into:

Wait — perhaps I misread. Let me interpret the tree structure logically.

Actually, standard phylogenetic tree reading:

The horizontal lines represent lineages, vertical lines represent branching points (nodes).

So:

Start from bottom:

Node 1 → splits into Bacteria and node 2
Node 2 → splits into Archaea and node 3
Node 3 → splits into Land plants and node 4
Node 4 → splits into Amoeba and node 5
Node 5 → splits into Shelled amoebae and Slime molds
Then back to node 3 → also leads to node 6
Node 6 → splits into Breviatea and node 7
Node 7 → has traits “Single flagellum, Insertion in EF1a gene” → then splits into:

- Capsaspora
- And a branch that leads to node 8 and node 10? No — actually, from node 7, one branch goes to Capsaspora, and another branch goes to a node that then splits into:

Wait — perhaps node 7 leads to a clade that includes:

- Capsaspora
- And then the rest: Fungi, Fonticula, Nuclearia, Choanoflagellates, Animals

Actually, looking at the diagram again (as described):

After node 7, there is a branch that leads to:

- Capsaspora (on one side)
- And on the other side, a branch that leads to node 8 (which gives Fungi, Fonticula, Nuclearia) AND also to node 10? That can’t be — nodes are branching points.

I think I need to reinterpret.

Actually, in the tree, node 7 is labeled with “Single flagellum, Insertion in EF1a gene”, and from node 7, there are three branches:

1. To Capsaspora
2. To node 8 (which leads to Fungi, Fonticula, Nuclearia)
3. To node 10 (which leads to Choanoflagellates, Sponges, Insects, Vertebrates)

Is that possible? In some trees, a node can have multiple descendants — but typically, a node represents a split into two lineages.

Looking at the way it's drawn, it's likely that node 7 splits into:

- One lineage: Capsaspora
- Another lineage: which then splits into node 8 and node 10? But that would mean node 8 and node 10 share a common ancestor at node 7.

Actually, that makes sense.

So:

Node 7 → splits into:

- Branch A: Capsaspora
- Branch B: which then splits at a new node (let’s call it X) into:
- Node 8: Fungi, Fonticula, Nuclearia
- Node 10: Choanoflagellates, Sponges, Insects, Vertebrates

But in the diagram, there is no node labeled between 7 and 8/10 — so probably, node 7 directly leads to three groups? That’s unusual.

Perhaps it's better to assume that the tree is structured as:

From node 6:

- Left: Breviatea
- Right: node 7

From node 7:

- One branch: Capsaspora
- Another branch: node 8
- Another branch: node 10

But that would make node 7 a polytomy, which is possible.

In that case, Choanoflagellates are under node 10, which is a direct descendant of node 7.

So, a monophyletic group including choanoflagellates could be the group at node 10: Choanoflagellates, Sponges, Insects, Vertebrates — common ancestor node 10.

Or, you could include Capsaspora and Fungi etc. by going back to node 7 — but then you'd have to include all descendants of node 7: Capsaspora, Fungi, Fonticula, Nuclearia, Choanoflagellates, Sponges, Insects, Vertebrates.

That’s also monophyletic.

Since the question says "of your choice", I’ll pick the smaller one: node 10 group.

Members: Choanoflagellates, Sponges, Insects, Vertebrates
Common ancestor node: 10

But wait — are Insects and Vertebrates both under node 13? Yes, but node 10 is the ancestor of all of them.

Yes.

Alternatively, to be precise, let's list:

At node 10, the descendants are:

- Choanoflagellates
- And the lineage leading to Sponges, then to node 12, which leads to Insects and Vertebrates.

So yes, all are descendants of node 10.

Perfect.

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Part c: Which node represents the most recent common ancestor of land plants and animals?

Land plants are shown at the bottom right — they branch off at node 3.

Animals are at the top right — they are under node 13, but their lineage goes back through node 10, 7, 6, etc.

To find the most recent common ancestor of land plants and animals, we need to find the node where their lineages last shared a common ancestor.

Land plants branch off at node 3.

Animals are part of the Opisthokonts, which branch off at node 6 (since node 6 leads to Breviatea and then to the opisthokont lineage).

So, the common ancestor of land plants and animals must be at node 3, because:

- Node 3 splits into Land plants and node 4.
- Node 4 leads to Amoeba, Shelled amoebae, Slime molds — and then further up to node 6, which leads to Breviatea and then to opisthokonts (including animals).

So, the lineage to animals goes: node 3 → node 4 → ... → node 6 → ... → animals.

Therefore, the most recent common ancestor of land plants and animals is node 3.

Because at node 3, one branch goes to land plants, and the other branch eventually leads to animals (via node 4, 6, etc.).

Yes.

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Now, let’s write the final answers.

Final Answer:

a. No, a group composed only of fungi and Fonticula is not monophyletic because their most recent common ancestor (node 8) also includes Nuclearia as a descendant, and excluding Nuclearia makes the group incomplete.

b. One monophyletic group that includes choanoflagellates is the group defined by node 10, which includes: Choanoflagellates, Sponges, Insects, and Vertebrates. The common ancestor is node 10.

c. Node 3 represents the most recent common ancestor of land plants and animals.