what makes a genus?

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MMark
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what makes a genus?

Post by MMark » Tue Aug 01, 2006 12:32 pm

Hi,
I tried to figure out what makes the boundaries of a genus and, to my surprise, there isn't any good information in wikipedia or other sources I found. The only thing I found was basically the info: its a taxonomic unit, it has subunits, genii (sp?) differ from one another- but not how.

So in case you know: what makes a certain genus distinct? Genetic match? Anatomic traits? Something entirely different?

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James
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Post by James » Tue Aug 01, 2006 12:58 pm

A genus is a taxonomic grouping comprising of closely related species. They are distinct through their common ancestry.

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Post by MMark » Tue Aug 01, 2006 1:05 pm

Thanks for your reply, but it doesn't really answer my question-
What does "common ancestry" really mean and how is it measured?
In other words, what do you measure to determine the degree of relatedness between two organisms and what is the threshhold to divide them into a different genus each? Mutations in certain key genes? Anatomical differences? Behaviour? Total genomic dna sequence overlap (unlikely)? Chromosome G-Bands?

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James
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Post by James » Tue Aug 01, 2006 1:18 pm

Common ancestry is when we attempt to find out how evolution created each new species and in what order. All the species in a genus will have a common ancestor, different from other genuses. Smaller categories nest within broader categories in the heirarchical system. In an attempt to measure relatedness we use morphology, ultrastructure, embyology, behaviour, fossils. DNA etc. I wouldn't say that there is a certain threshold but we attempting to create an evolutionary tree, and in this process we create the categories ie species, genus, family etc through examining evolutionary relationships.

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MrMistery
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Post by MrMistery » Tue Aug 01, 2006 6:27 pm

I think his point is this: Human and tiger have a common ancestor different from other organisms and human and Homo erectus have a common ancestor different from other organisms. So how do you determine how long ago in an ultrameric tree the last ancestor has to be. it is a good point actually
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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pankaaj
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Post by pankaaj » Fri Aug 04, 2006 1:18 pm

Differentiation will ultimately differentiate the ancestors also!
Take it with a pintch of salt!

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