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wrote...
Posts: 20623
6 years ago Edited: 6 years ago, bio_man
Step 1. Pick your organisms (I’m going to pick a lemur, deer, cow, chimpanzee, human, and lizard). The taxon (group) which all of these organisms have in common is the phylum Chordata. If we removed the lizard – hypothetically speaking – the taxon would be the class Mammalia.

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Step 2. List as many possible characteristics the organisms possess (five is typically ideal, but you could pick >5 if you really wanted to; the more you choose, the more accurate your cladogram). I’m going to pick: [/font][/size]

• Five digits
• Hair
• Tail
• Opposable Thumbs
• Placenta

This goes on the first row, while the organisms we chose go into a column on their own.

Here is a list of things you can choose:

 Also:

Step 3: Use some logic and pick which organism in the group would be considered the outgroup. In other words, which one, in your opinion, is least common to the rest. It’s really important that you think this through because it will significantly determine how your cladogram will turn out. Using some logic, it seems like the lizard, which is a reptile, is least common with all the rest (the rest are obviously mammals).

Now that we’ve distinguished the reptile as our outgroup, let’s look at the five characteristics we decided to focus on, namely, five digits, hair, tail, opposable thumbs, and placenta.

Make a small list like this:

Using this information, we can judge which trait is the more recently derived trait. This can usually be done by comparing the traits with the outgroup (our lizard). What this means is that since the lizard is our outgroup – the one that is least related – the shared derived characteristics we’re going to choose will be the opposite of what our lizard possesses. For example, the lizard has 5 digits (a primitive condition), so the shared derived characteristic will be “Does not have 5 digits”. The lizard has no hair (a primitive condition), so a shared derived characteristic will be “Has hair”. Having a tail is a primitive condition, so a shared derived characteristic is “Has no tail”. Has no opposable thumbs is a primitive condition, so a shared derived characteristic is “Has opposable thumbs”. And finally, Has no placenta is a primitive condition, so “Has a placenta” is a shared derived characteristic. Remember that shared derived characteristics are called synapomorphies. We can start building our table.

Now fill it in. If the organism has the shared derived trait, put a plus (+); if the organism does not have the shared derived trait, put a minus (-).

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wrote...
6 years ago
Step 4.

 Draw a “V” with the outgroup at the upper left. The base of the V represents the common ancestor to all animals.

Step 5. All the animals except for the lizard have a placenta and have hair. Therefore, the first shared derived characteristic on our cladogram will be placenta and hair. If, for instance, we had a condition where one mammalian organism we had chosen did not have hair, we would have to use some logic when determining which characteristic evolved first. That is, did the placenta come first or did the hair? Since hair is a characteristics of nearly all mammals (except for whales, dolphins, etc.), we could safely say that the placenta came first, and then hair, so you would have a branch for placenta first and a branch indicating the presence of hair second.

Step 6. We only have three characteristics left, namely, having opposable thumbs, having no tail, and have <5 digits. If we look at our chart, we’ll find that having opposable thumbs is shared by three organisms, whereas having <5 digits and no tail is shared only by two. The lemur, human, and chimpanzee all have this shared derived characteristic and so should be in a branch on their own. However, since both humans and chimpanzees don’t have a tail, that branch will further branch off into non-tailed organisms possessing opposable thumbs.

 Or, the one to your is the more conventional method due to parsimony; parsimony is a principle that says that you should use the simplest explanation when constructing your tree. This means that we should create our tree using the least possible steps.

Step 7. Make a conclusion. Based on the complete phylogeny, we can infer that the cow and the deer are more closely related to each than to other groups. Similarly, humans and chimpanzees are more closely related to each other than to other groups. We can also conclude that lemurs are more closely related to chimps and humans than to cows and deer.
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