Question

Im having troubles with my AP Bio cladogram. Its just not coming out the way it should! For my cladogram, what should i do if there are two organisms with the same characteristic? And if you put a characteristic at the beginning of the line, does that mean ALL of the organisms have it? Please help!

Answer 1

For two organisms with the same characteristic, try and find some factoid that differentiates the two. If there is none, you can make a single line that branches into two. Like the two ends of the letter Y, if that makes sense.
I believe that if there's a characteristic at the beginning of the line, it means all following have it. In a cladogram, you try and seperate organisms based on characteristics that get more and more specific.
Like, if you ever played the game 'Guess Who', or '20 Questions', you first ask a really general question that immediately divides a group (like, 'is this person a boy or girl') and later have something more specific ('do they have a freckle on their chin?')
If that makes sense.
Good luck!

Answer 2

If two organisms have the same characteristic, that means that either they're closely related (e.g. they're sister taxa), or the same characteristic has evolved separately (convergent evolution). Here are the two options:


(I don't know if the K! is how you indicate convergence in English. It's just what my German prof does.)

You can tell the difference by looking at other characteristics and also at the other species/taxa involved. If you see two species that have a lot in common, they're probably related, but if they have only one or two things in common and have a lot more in common with other species that don't have the characteristic you're looking at, the characteristic probably evolved convergently.

An example would be bird beaks and the beak of the duck-billed platypus. It's basically the same structure, made of basically the same material, but we know it evolved convergently because a platypus has hair and milk glands and a whole bunch of other characteristics that make it more mammal-like than bird-like, and the hypothesis that maybe the common ancestor of birds and mammals had a beak doesn't work because other mammals and reptiles (more closely related to birds than mammals) don't have beaks. If you assumed that beaks did NOT evolve convergently, you'd have to also assume that the characteristic was individually reduced in every single non-beaked reptile/mammal species, and that's very unlikely.