Animal Polyploidy: A Mechanism for Evolution?

(R. Joel Duff) #2

Last line summarizes the YEC approach to all possible examples of genome evolution.

“Though possibly providing more potential for variation within a kind, it does not provide novel specified genetic information. To use a book analogy, extra copies of old chapters (polyploidy) do not create new chapters (new specified genetic information). Regardless of whether it is ultimately classified as deleterious, neutral, beneficial, or all the above depending on the species, polyploid speciation is consistent with the creationist worldview.”

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(S. Joshua Swamidass) #3

Those extra copies, however, work great at preventing “devolution”.

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(John Harshman) #4

They also seem to work well at promoting differentiation and complexity, as witness the two rounds of duplication in vertebrates (three in teleosts) of the originally single Hox cluster.

(S. Joshua Swamidass) #5

Remember Ohno’s 2R hypothesis, which is now solidly validated.

(Curtis Henderson) #6

Reeeeeeeally late to the conversation here, but I didn’t catch this post and thread earlier. @davecarlson and @evograd, is this a central piece in evolutionary biology education at this point? I never had a class on the topic and it escaped my attention until a student asked me about it this morning. I had a hunch (correctly) it might have been mentioned here before. Also, is there some evidence supporting a widespread tetraploid “trend” in the past?

(Blogging Graduate Student) #7

Which part do you mean? The 2R hypothesis is obviously pretty mainstream by now, and polyploidy and it’s effects are taught about in general.

(Dave Carlson) #8

I’m not aware of any particular “trend”. Polyploidy is, like all mutations, something that just happens occasionally during cell division. Most of the time it probably is not helpful, but occasionally it is. There has been a lot of speculation regarding the notion that polyploidy could be an important contributing factor to certain adaptive radiations, but as far as I’m aware, it’s still primarily speculation.

Interestingly, there does seem to be a general trend toward “diploidization” after polyploidy, where many duplicated gene copies and even whole chromosomes are eventually lost, and normal chromosome pairing during meiosis is restored.

(Curtis Henderson) #9

Basically, even though I knew there were a few examples like Xenopus, I hadn’t realized that it was thought to be a rather prominent feature in early vertebrate evolution. From the tail end of the Wiki article:

The controversy raging in the late 1990s was summarized in a 2001 review of the subject by Wojciech Makałowski, who stated that “the hypothesis of whole genome duplications in the early stages of vertebrate evolution has as many adherents as opponents”.[5]

In contrast, a more recent review in 2007 by Masanori Kasahara states that there is now “incontrovertible evidence supporting the 2R hypothesis” and that “a long-standing debate on the 2R hypothesis is approaching the end”.[22] Michael Benton, in the 2014 edition of Vertebrate Palaeontology , states, “It turns out that, in places where amphioxus has a single gene, vertebrates often have two, three, or four equivalent genes as a result of two intervening whole-genome duplication events.”[23]

Is that a good summary of the current state of the hypothesis?

(Dave Carlson) #10

I don’t think there is much lingering doubt regarding the existence of a whole genome duplication in the ancestor of vertebrates. It’s the significance of this and other polylploidy events that is still debated.

While it’s not entirely germane to this topic, my PhD advisor has a nice review regarding the cellular challenges of coping with polyploidy that you can read here.

(S. Joshua Swamidass) #11

@cwhenderson the issue is not that this is pervasive or common but that evidence of two specific whole genome duplications is pervasive, even though it was just two events, and therefore very rare.

(Curtis Henderson) #12

Right, so a whole-genome duplication (or two) relatively early in chordate history would have a significant impact on all vertebrates. So the frequency isn’t important, but the timing is. Am I reading that correctly?

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(John Harshman) #13

Three, counting the extra one in teleosts.

(Blogging Graduate Student) #14

Yes, I’d say it’s now pretty undeniable that there were 2 rounds of genome duplication early in vertebrate evolution.

(Dave Carlson) #15

Apropos of this discussion, I attended a weekly seminar today on the topic of yeast evolution and learned that the ancestor of fermenting yeast experienced a whole genome duplication event around the same time period in which the clade diversified. In addition, the strains of Saccharomyces that are used in brewing (but not in wine-making) are generally triploid or tetraploid.

I don’t know what exactly the significance of this is, but it’s interesting!

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