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I have this paragraph that i have halfway finished, but i do not know what to put in the spaces.


A Cladogram is a branching diagram that represents the proposed phylogeny or evolution of a species or a group. The groups used in Cladograms are called clades.. To construct a cladogram, two characters are defined. Then the outgroup of various species are identified based on the sequencing or closeness of the derived characters in the clades. In making a cladogram, ______ assume that groups that _____ more derived characters have a more close common ancestor.


The letters that are italicized are words that i think are correct. This paragraph is needed for part of a recite that i have to do in front of my class. The prof. gave me a page like this. And I don't know what those spaces are. Can someone help me.. please?

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closed as off-topic by AliceD, canadianer, Chris, WYSIWYG, fileunderwater Mar 2 '15 at 9:41

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy." – AliceD, canadianer, Chris, WYSIWYG, fileunderwater
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Maybe: construct=infer, two=homologous, outgroup=ancestors, sequencing=presence, closeness=absence, clades=clades, _____(1)=always, ______(2)=share, close=recent. The last sentence assumes you are only considering maximum parsimony. $\endgroup$ – mcg256 Mar 2 '15 at 1:58
  • $\begingroup$ ok, this is to all the people that put this on hold HAVE shown an attempt to answer.my answers are the ones in ITALIC. So, can you please explain to me why you put it on hold? Because clearly, you can see the italic words. $\endgroup$ – Csharper Mar 2 '15 at 23:22
  • $\begingroup$ @mcg256 thanks. and thank you for the explanation, you are very kind. $\endgroup$ – Csharper Mar 2 '15 at 23:22
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I provided some edits in my comment -- hope the following clarifies things for you a little bit.

To construct a cladogram, two characters are defined.

You may be confusing character and character state. It's valid to have a cladogram with a single character (e.g. the single character, "warm-blooded"), but you will need at least two character states to infer a non-trivial cladogram. The states for the character warm-blooded would be Yes or No.

A molecular example would be a cladogram inferred from a column of a sequence alignment. That column is the character, and for, say, DNA, the character states are the set {A,C,G,T}.

Then the outgroup of various species are identified based on the sequencing or closeness of the derived characters in the clades.

The outgroup is specified by you, the investigator. It's typically a hypothesis (viz. model parameter), which is either a guess or is based on some external evidence.

In short, the analysis starts from character-state data for some number of taxa ("species" in your paragraph). From this data you are selecting (constructing) a tree-topology that best fits this data.

E.g. for four taxa, labeled A,B,C,D, with D the outgroup, the process is like:

 start  --> cladogram
 ABC(D)     A  B C (D)
             \/ / /
              \/ /
               \/

There are many different methods to construct the cladogram. One popular method is maximum parsimony, but the assumptions of that model are severe. However, any method is effectively selecting a tree topology out of all the finitely-many possible tree topologies over N leaves, where N is the number of taxa (species) in your investigation.

In making a cladogram, ______ assume that groups that _____ more derived characters have a more close common ancestor.

In this sentence, you seem to be expressing a relationship between the number of shared derived characters (synapomorphies) for a given clade, and the common ancestor of that clade.

This can be very confusing, maybe an example will help. Let me annotate the above tree with a binary character, having states + and -.

            +   +  -   - 
            A   B  C  (D)
             \ /  /   /
              +  /   /
               \/   /
                -  /                   
                 \/
                  -

The idea is that the ancestral state for the entire group is -, as was the state for the ancestor of {A,B,C}. However, the + state was derived after the ancestor of {A,B,C} but before (or "in") the ancestor of {A,B}. Then it was passed to the terminal units, A and B. (Note: typically you don't have this ancestral-state information, only the information at the tips of the tree. You're actually inferring the ancestral states and topology from the data at the tips.)

I would claim that, in general, taxa that share more derived character (states) have a more recent common ancestor than taxa that do not. Although, this can be confounded by homoplasy.

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  • $\begingroup$ thanks for the in-depth explanation. you deserve more than one upvote! Not enough thanks to be given. $\endgroup$ – Csharper Mar 2 '15 at 23:25

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