Pharyngula

Evo-devo on NOVA

Don’t miss it! Tonight at 8pmET/7pm Central, NOVA is showing What Darwin Never Knew, a documentary about evo-devo. I shall be glued to my TV tonight!


I just started watching it. So far, it’s a nice little history of Darwin and his ideas; Sean Carroll is a good person to have talking up the story. It’s nothing new yet, and nothing about evo-devo so far — I’m waiting impatiently for it.


Twenty minutes in, we get a little embryology: limb rudiments in snake embryos, tooth rudiments in whale embryos, and branchial arches in human embryos. These are shown as uncompromising evidence of limbed, toothed, and gilled ancestors — cue wails of horror from the Discovery Institute…now.

They also discuss variation in dog breeds. More development, please!


Hmmm. We’re past the half-hour mark, and it’s all selection, selection, selection. It’s clearly explained and it’s a useful intro to the general concept of Darwinian evolution…but I was hoping for something a little more focused and novel. This documentary is supposed to be based on Carroll’s Endless Forms Most Beautiful and The Making of the Fittest, but we’re getting bogged down in very general material and not yet getting to the meat of either book.

Now we’re getting an explanation of DNA sequences as a code (alarms are whooping at the Discovery Institute again), with pigment changes in different varieties of mice as an example. We’re also getting brief mentions of genetic changes that produce color vision and cold-adaptedness in icefish (those are straight from Making of the Fittest).


This bugs me. They’re talking about the number of genes in the human genome as a big surprise — we “only” have 23,000 genes. I don’t know; it always seems to be dropped out of context. How many genes should we have expected?


Some nice animations of transformations of embryos are shown, illustrating (as Haeckel did) that all vertebrates began with a common body plan that diverges in detail over the course of development — I hope an ambulance is on standby in Seattle near the DI.

Unfortunately, they’re using developmental changes as an explanation for why we have too few genes to satisfy our egos. Again, this bugs me: fruit flies and people have comparable numbers of genes, and also comparable developmental processes.

Anyway, it does lead into some useful discussion of evolving pigmentation spots in Drosophila, which leads further into regulatory DNA. Unfortunately, this bit has some confusing stuff. The documentary conflates regulatory DNA with junk DNA — regulatory is not and has not been regarded as junk! — and might lead some viewers into thinking that all junk DNA has developmental functions. It does not.

They do have some nice illustrations of experiments used to tag regulatory sequences with marker genes, making flies with glowing spots on their wings.


Another good example: they’re showing the evolution of regulatory switches in stickleback fish. Cool, it’s David Kingsley! They’re showing how the differences between marine (spiky) and freshwater (non-spiky) is not in the coding sequences of a few genes, but in the regulatory regions of those genes.

Hmm. Repetitive flashy graphics of DNA are beginning to hurt my eyes.


We also get a summary of Tabin’s work on the genes behind different beak morphologies in finches. The same genes are involved, but the differences are in the timing and strength of activation of these genes. The genes involved are also explained as regulatory genes — the genes that switch other genes off and on. This is starting to get into stuff I’d find useful in the classroom.


Hey, now it’s Neil Shubin’s turn to talk about the evolution of limbs. This show is turning out to be a nice introduction to the superstars of evo-devo!

More cool stuff: video from Ellesmere Island, and the discovery of Tiktaalik. Also an amusing animation of the fossil coming to life in Shubin’s lab, which I’m pretty sure doesn’t actually happen.

The show quickly moves from fossils to molecules, and describes efforts to isolate the limb regulatory pathway from modern relatives (paddlefish) of the ancient tetrapods. We get to hear a little bit about Hox genes. Oooh, I could use some of those sequences illustrating the pattern of Hox gene expression in the limb…

We don’t need new genes to make new structures: changing the timing and strength of expression of genes within an existing pathway can create new features.


At least, a clear statement of what Darwin didn’t know that the documentary is describing: we are deriving mechanistic explanations for the processes that produce morphological diversity. It’s a consequence of subtle shifts in the timing and intensity of gene expression in a hierarchy of well-established functional pathways.

We’re getting into the last half-hour here, and the emphasis is switching to humans. Ho-hum. Humans are really crummy experimental models, so I guess we’re not going to get deeper into those mechanisms, but will tap into the audience’s self-centeredness, which they need to do, I guess.

At least they’re focusing a bit: they promise to tell us about the genetics of hand development, and specifically of the thumb. They’re scanning genes that are different between humans and chimpanzees, looking for molecules that suggest they play a role in the differences in digits. A gene is found that is active in the thumb and big toe, and also differs significantly in sequence between us and the chimps. This is work I’m unfamiliar with — it would be nice if they named the gene for us!

Noooo…we’re teased with some interesting work, and now it’s flitting off to talk about the brain.


Another tease: a researcher identifies a gene that differs between humans and chimpanzees, and is defective in humans; it’s involved in chewing muscles. It is suggested that knocking out this gene was part of the process of freeing up the expansion of the cranium. It’s a frustrating part of the medium that it makes it hard to dig up more specific citations. (OK, here’s a short article on Stedman’s work).

They do it again with a regulator of neuronal growth involved in microcephaly: name the gene, please. They keep talking around it, calling it “this gene” or “the key gene”. It’s just odd that they ignore one of the conventions of molecular biology, failing to give us a name that we can use as a handle. It’s going to make it difficult to talk about over the water cooler tomorrow, isn’t it?


Olivia Judson relates it all back to Darwin: he was the beginning, not the end of evolutionary biology.


My opinion overall: the first half hour was boring to me — it was an extremely basic primer in old-school Darwinian biology. The middle hour was of more interest, and did get into real evolutionary developmental biology, and showed off some of the best examples of work in the field. This was the bit I’d find most useful in my classes; that first half-hour was too basic for most freshman biology majors.

I wasn’t too keen on the last bit where it got very human-centric, but I can see where the examples they talked about would provoke viewer interest. I just wish it were possible for the medium to push a little deeper into the topics than they did.

Carroll, Shubin, and Tabin were good. Make them TV stars!

Comments

  1. #1 Glen Davidson
    December 29, 2009

    And if you’re special, an IDiot or other creationist, you still fail to know it. Or at least, to grasp the implications.

    We can be assured that few cretins/IDiots will trouble to learn such evil, waiting instead for the mendacious account of it that the DI’s CSC (for which Meyer is responsible) will put out.

    Glen D
    http://tinyurl.com/mxaa3p

  2. #2 Naked Bunny with a Whip
    December 29, 2009

    I shall be glued to my TV tonight!

    You host the best play parties, PZ.

  3. #3 Newfie
    December 29, 2009

    Yay… I get this show on my Detroit affiliate. Thanks for the heads up, PZ.

  4. #4 F
    December 29, 2009

    Sweet.

  5. #5 nejishiki
    December 29, 2009

    How soon until a creationist claims that the show refutes Darwinism?

  6. #6 NewEnglandBob
    December 29, 2009

    I will be glued to my DVR…oh wait, I don’t have to watch it tonight.

  7. #7 Naked Bunny with a Whip
    December 29, 2009

    @NewEnglandBob: Plus you’ll be able to skip all those annoying commercial breaks.

  8. #8 Kel, OM
    December 29, 2009

    See? Darwin was wrong! Evolution is a lie and Nova is exposing it!!! Though Darwin did know that the fossil record is incomplete, so this must be something else showing God’s work! I knew the eye was irreducibly complex… ;)

  9. #9 destlund
    December 29, 2009

    Awesome! Just in time. Thanks, PZ!

  10. #10 Rotting in the Midwest
    December 29, 2009

    I’ll be waiting for it to hit youtube!

  11. #11 Antiochus Epiphanes
    December 29, 2009

    I will be continuing my science beg-a-thon this evening. Thank (whomever invented the DVR) for my DVR!

  12. #12 God
    December 29, 2009

    Great! Reading this blog was starting to make Me doubt My own existence, but it feels so reassuring to know that Darwin wasn’t omniscient. Now My faith in Myself is again as strong as ever.

  13. #13 Sven DiMilo
    December 29, 2009

    Darwin knew all about evo-devo. It’s all there in one of his lesser-known books, On the Tendency of Inherited Gemmules to Behave as Hierarchical Developmental Switches; or Miscellaneous Contributions to the Study of Homeobox Thingamajobbies (1877).

  14. #14 tdcourtney
    December 29, 2009

    I had the same thought, I hope some creationist followers tune in expecting Darwin to be refuted. They might accidentally learn something.

  15. #15 SC OM
    December 29, 2009

    Have it on!

    Fucking ads on fucking public television.

    *grumble*

    Will you be liveblogging?

  16. #16 SC OM
    December 29, 2009

    That was funny what they just did with his face.

  17. #17 Insightful Ape
    December 29, 2009

    OK one error already.
    In the chapter one of the Origins Darwin argues that the way dog breeders develop new features is not by crossing the already existing traits. Rather, it is by taking a characteristic and running with it-breeding dogs with a certain feature among themselves, and repeating the cycle.
    This is not what “What Darwin Never Knew” said.

  18. #18 SC OM
    December 29, 2009

    Oh! It’s two hours long!

  19. #19 Biology Blogger
    December 29, 2009

    Extremely interesting. Though they need to stop focusing on Carrol. They need some new faces, and now before I watch old family guy episodes on hulu!

  20. #20 Doktor Zoom
    December 29, 2009

    Err, did I just hear the narrator say “from the leopard…” over a stock footage shot of a cheetah?

    Clearly, your evolution is all a lie!

  21. #21 Rorschach
    December 29, 2009

    I will be taking “Endless forms most beautiful” to the beach with me now instead !

  22. #22 Newfie
    December 29, 2009

    I haven’t learned anything new so far, but it’s really engaging, and has reinforced my understanding. How do I donate money?

  23. #23 skeptical_hippo
    December 29, 2009

    I adore the tiktaalik animations. I want a compilation of those as a screensaver.

    Shubin’s Inner Fish book is what initially got me interested in evo-devo. The embarrassing truth is I was browsing the new arrivals at the library, saw the title on the spine, and only pulled the book off the shelf because I thought it’d be about improving my swim stroke. :) When I saw what it was about, I thought “what the heck, this could be an interesting read,” and checked it out anyway. Lucky find for me.

  24. #24 Biology Blogger
    December 29, 2009

    Shubin just had me glued for 20min. I did not even respond to facebook comments. Thanks Neil!

  25. #25 Rutee, Shrieking Harpy of Dooooom
    December 29, 2009

    What’s “evo-devo” supposed to mean?

  26. #26 Biology Blogger
    December 29, 2009

    Evolutionary Developmental Biology, I believe.

  27. #27 Newfie
    December 29, 2009

    This show is dumbed down, and meant to raise awareness in the segment of the population that questions/doesn’t understand evolution.

    I’ve been out of grade school for some time now, but shouldn’t this be basic to a first year high school student now?

  28. #28 Antiochus Epiphanes
    December 29, 2009

    They’re talking about the number of genes in the human genome as a big surprise ? we “only” have 23,000 genes. I don’t know; it always seems to be dropped out of context. How many genes should we have expected?

    At the time we would have expected that the number of genes would have been about equal to the number of proteins in the proteome. However, there are more proteins than genes (not including immunoglobins, even). Did they talk about alternative splicing of genes?

  29. #29 monado
    December 29, 2009

    Recording the last half hour while LotStreetWiz watches college football. But it’s past his bedtime; I’ll be able to watch it as soon as football ends.

  30. #30 DanielR
    December 29, 2009

    I’m drooling… A documentary about evolution combined with brain science… I am in neuroscience heaven.

  31. #31 Insightful Ape
    December 29, 2009

    OK, this was interesting.
    A few problems-a little too anthropocentric.
    Not much stuff about development.
    Almost all of first hour had very little new for anyone with a casual interest in the subject.
    With all that said, it was quite interesting-
    will be waiting for the frauds at discovery institute to come up with their rebuttal.

  32. #32 TimK
    December 29, 2009

    When did Paddlefish become close relatives of Tetrapods?

    Lungfish aren’t sexy enough for Public Television evidently.

  33. #33 chuckgoecke
    December 29, 2009

    When I was in undergraduate, the cool tee-shirt to have, amongst the bio-nerds stated: “ontogeny recapitulates phylogeny”, which I guess isn’t cool anymore(because its wrong). It was the tee to counter the English nerds “Eschew Obfuscation”. I was easily entertained back in those days.

  34. #34 Sven DiMilo
    December 29, 2009

    Make them TV stars!

    Yeah, there could be this apartment where 3 bionerds live and talk about evo-devo all the time, and act like total nerds, and use the correct names of genes and stuff, and then they could be contrasted for comic effect with the beautiful female neighbor who doesn’t have much book learning but has feisty street smarts and a heart of gold. We’ll call it, uh, “The Hox Box.”

    Right now it’s only a notion, but I think I can get the money to make it into a concept, and later turn it into an idea.

  35. #35 amphiox
    December 29, 2009

    I’ve been out of grade school for some time now, but shouldn’t this be basic to a first year high school student now?

    Not in America, it would seem.

    And we all know why.

  36. #36 amphiox
    December 29, 2009

    It looks like to me that pretty much everything is coming out of Carroll’s two books “Endless Forms Most Beautiful” and “Making of the Fittest”. The Paddlefish example, for instance.

    Of course, for lots of it, Carroll’s books are secondary/tertiary/quaternary sources.

  37. #37 Sven DiMilo
    December 29, 2009

    When did Paddlefish become close relatives of Tetrapods?

    I was wondering about that choice too. Extant lungfish have pretty crappy excuses for fins except for the Aussie ones. Probably they are interested in the ancestral fin-development pathway for tetrapods and think that paddlefish, as relatively primitive ray-finned fishes, might retain aspects of that genetic pathway that have been lost in lungfish and more derived actinopts.

  38. #38 amphiox
    December 29, 2009

    The Paddlefish examples comes from Carroll’s books. I can’t remember precisely (as it’s been a while since I’ve read them), but the reasons for using Paddlefish that were given were largely pragmatic ones – ie they were convenient model organisms to experiment on, for various reasons.

  39. #39 neurotick9
    December 29, 2009

    we all need to remember, these shows target, if not the lowest common denominator, then a very low denominator. They ain’t meant for grad students or post docs, etc. They are meant for the general public with little or no working knowledge of the subject.

  40. #40 mythusmage
    December 29, 2009
  41. #41 DanielR
    December 29, 2009

    I thought the show was great. Very good material to show to those family members that think that there is no evidence for evolution. Not much new information, but good for an introduction.

  42. #42 https://www.google.com/accounts/o8/id?id=AItOawk8VcTSPyM3S1oPFBPbKvIeNynyhq9s0IY
    December 29, 2009

    A little too anthropocentric, but overall pretty good. I’ve kept up on this stuff — through the popular literature, since I studied CS instead of biology — so nothing was really new to me. However, for someone who hasn’t been keeping up this presented the current research areas in evolutionary biology quite well.

    Things I liked: almost an hour on evo devo. The bit from the neurologist talking about he never thought he would be lead into studying evolutionary biology from his work on microcephalics. This just shows the explanatory and organizing power of evolution in the biological sciences. Tiktallik overturning the glassware in Shubin’s lab.

    Things I didn’t like: the first 1/2 hour. I learned this stuff in high school and I’ve read Origin. And they left out all of Darwin’s painstaking research on barnacles — this was great stuff, why ignore it? The anthropocentric stuff. This could have been more interesting if it had focused on specific areas of brain morphology rather than just size.

    Overall, though, given the target audience I have to give this one an “A”. Please, tell me more!

  43. #43 https://www.google.com/accounts/o8/id?id=AItOawk8VcTSPyM3S1oPFBPbKvIeNynyhq9s0IY
    December 29, 2009

    Egads, why doesn’t scienceblogs get the nom de blog from the Google account information. Bad programmers, bad.

  44. #44 F
    December 29, 2009

    I can’t go back through the insanity, but there is a way to make it present your name properly.

  45. #45 Rorschach
    December 30, 2009

    Did the program mention the interesting question that Carroll raises in the book?

    Is a zebra black on white or white on black?

    Discuss…:-)

  46. #46 Katrina
    December 30, 2009

    I have to wait until it comes on on-line. :-(

  47. #47 Sylvie
    December 30, 2009

    The music and repetitive exploding switches on DNA strands were almost enough to make me turn it off (maybe I’m old fashioned but I preferred the more understated approach of old Nova shows) but I did think that Neil Shubin and his Tiktaalik were instant TV stars.

  48. #48 Antiochus Epiphanes
    December 30, 2009

    I am watching it now…irked. Darwin was not the first to propose that species change, although this is precisely what this documentary says. Buffon? Lamarck? Shit sake, his grandfather? Evolution was already an explanation for diversity when Darwin hit the Galapagos. …No wonder my students don’t get this.

  49. #49 F
    December 30, 2009

    Is a zebra black on white or white on black?

    Or quite possibly Wu.

  50. #50 JamesBrown
    December 30, 2009

    Well I loved the show.

    That’s the great advantage people like me have over experts in the field. We are seldom disappointed and always amused.

  51. #51 Modeler
    December 30, 2009

    a researcher identifies a gene that differs between humans and chimpanzees, and is defective in humans; it’s involved in chewing muscles. It is suggested that knocking out this gene was part of the process of freeing up the expansion of the cranium.

    Richard Wrangham proposes a wonderful hypothesis in “How cooking made us human” – that the chewing muscles were reduced because early homo was eating cooked/prepared food.

    Cooked food is significantly easier to eat (we spend about one hour a day eating as opposed to daily 6 hours of constant chewing required by the uncooked diet of chimpanzees and gorillas) and from which we gain significantly more energy (up to 25%).

    In obtaining much more energy from a given piece of food, we have evolved a shorter gut than other animals. Guts are expensive things to run, so the freed-up energy is now available for such things as growing large, expensive brains.

    So the gene knockout has the same phenotypic effect – growing larger brains – but has a much more interesting story to tell of human evolution.

  52. #52 Kel, OM
    December 30, 2009

    Sounds interesting, will suck it down when I can find it online.

  53. #53 Modeler
    December 30, 2009

    And the gene’s name (for the reduced jaw muscles) is MYH16. Our allele is thought to have originate some 2.5mya, but maybe as early as 5.3 (Stedman et al., “myosin gene mutation correlates with anatomical changes in the human lineage, Nature, 428:415-418, 2004)

  54. #54 atheistyogi.com
    December 30, 2009

    The tiktaalik pushups were so cute :)

    I was expecting a bit more on embrioe development. Just about only thing they talked about there was “gill slits”…

    I am total agreement on the “gene switch” graphics. The flash was kinda annoying after the second time and the big red button looked like a panic button to me. LOL

    The most surprising thing to me was the bit about the ‘defective’ genes for the jaw muscles. I’ve only got a lay understanding of genes and such, but how could a base pair be actually missing a letter? Wouldn’t the missing letters be filled in as soon at the DNA was split apart and replicated? If anyone can send more information on this I would be very interested.

  55. #55 brotheratombombofmoderation
    December 30, 2009

    The human-centric stuff does make sense — non-humans generally don’t respond well to PBS pledge drives.

  56. #56 atheistyogi.com
    December 30, 2009

    Humm, and one more question the documentary did not address.

    Did the female fruit flies like the glowing wing spots on the males?

    :)

  57. #57 Baccala
    December 30, 2009

    Thought it was good enough for the masses and my worst fears – something I was waiting for – something I felt just had to be slipped in for Congress-sake – some tasty bone – some mitigation – some hope – thrown to the godiots that implied the controversy – and the role of religion in understanding the almighty WHY.

    I was expecting at least some cut to a religious biologist that although true to the facts would have some comment in some sly fashion that the “wondrous hand of god made all this, praise the lord”

    I did not see any of that – to my pleasant surprise – but I am old and several BR breaks were undertaken.

  58. #58 Rob in Memphis
    December 30, 2009

    Well, they showed it here on our local PBS station, which will probably have the local religious whackaloons up in arms, so they’ve decided to follow it up with the six-year-old, two-part documentary Peter and Paul and the Christian Revolution tonight.

    They also air an hour-long show called Classic Gospel a couple of times a week, but do we get two hours of science programming to offset it? Of course not. >:-(

  59. #59 Rob in Memphis
    December 30, 2009

    Sorry, that should’ve read “…two extra hours of science programming….”

  60. #60 JackC
    December 30, 2009

    I REALLY wish they would knock of the “.. xxx was a quantum leap …”

    JC

  61. #61 David Marjanovi?
    December 30, 2009

    Is a zebra black on white or white on black?

    White on black, as shown by all other horse species.

    Tree-thinking, people.

    how could a base pair be actually missing a letter? Wouldn’t the missing letters be filled in as soon at the DNA was split apart and replicated?

    DNA repair is not part of replication; if such a situation hasn’t been repaired, you end up with two different single strands, and replication makes two different double strands out of them, one with one fewer base pair than the other.

  62. #62 Yubal
    December 30, 2009

    This bugs me. They’re talking about the number of genes in the human genome as a big surprise ? we “only” have 23,000 genes. I don’t know; it always seems to be dropped out of context. How many genes should we have expected?

    Huh?!?

    I guess most people are still pissed off the fact that ordinary lettuce has much more genes than we do :/

    Dunno if Stephen Meyer touched that issue in his infamous book. Has anyone here read Signature in the Cell? I’d be curious to learn how the other side deals with this, quite frankly embarrassing fact. ;)

  63. #63 Antiochus Epiphanes
    December 30, 2009

    Yubal #62…
    I kind of dealt with this in #28, but admittedly didn’t get far enough in last night’s viewing to get the answer. I was too irritated by the conflation of evolutionary thought with Darwinian selection. When I finish round #6 of my beg-a-thon this evening, I’ll check out the rest.

  64. #64 atheistyogi.com
    December 30, 2009

    Thanks David Marjanovi?.

    My confusion was probably due to the way the missing letters were displayed in the graphic…since the graphics are usually oversimplified and sometimes perhaps not very accurate. But then again, my own understanding of DNA is incredibly basic anyway.

  65. #65 Yubal
    December 30, 2009

    #61 David Marjanovi?

    DNA repair is not part of replication

    Are you sure? I mean, one can not work without the other…. How about Recombination dependent replication ?

    #63 Antiochus Epiphanes

    Yeah, later. Also check out this guy here who needs(?) more than 1000 Chromosomes: Ophioglossum

  66. #66 ott.tom
    December 30, 2009

    I found last night’s program to be really interesting and enjoyed watching it. I particular like the theory about how we developed large brains due to the mutation in the jaw muscle and how they figured out what triggered opposable thumbs.

    There will be reruns over the next two days and I plan on watching it with my 4 yo daughter who is fascinated by DNA and genes. Strange interest for a 4 yo but I’m encouraging her to follow her interests.

  67. #67 Antiochus Epiphanes
    December 30, 2009

    @Yubal (hee-hee)…yeah, but those chromosomes are duplicated to the nth degree and are super-tiny. The point you are making* is well taken. There is a single-celled radiolarioan, Aulucantha scolymantha that beats Ophioglossum with a diploid number of ~1600. Meanwhile, the lowly male jack-jumper ant (Harpegnathos saltator) has just one chromosome (he’s haaaaappploooooooidddd!)

    *Number of chromosomes/genes not proportional to perceived complexity? Am I catching your drift? Or possibly God’s love not proportional to chromosome counts?

  68. #68 David Marjanovi?
    December 30, 2009

    DNA repair is not part of replication

    That is, errors that are made during replication are for the most part repaired during replication; older errors, however, are not repaired during replication.

  69. #69 Rorschach
    December 30, 2009

    White on black, as shown by all other horse species.

    Carroll’s answer is, it’s got both white and black stripes.
    Apparently the answer depends on whether the white areas of the skin have melanocytes that are inactivated/turned off/not producing black pigment, or not.

  70. #70 prostock69
    December 30, 2009

    This was an amazing show. Hubby and I are not very knowledgeable regarding evolution. We learned an incredible amount of info that we will be sharing with our families. I can’t wait for my dad to watch this. He doesn’t understand science which causes him not to trust it. This program will help immensely in giving him a good understanding of what evolution is and the science behind it AND how we know it’s true and not just a “theory”.

  71. #71 Rorschach
    December 30, 2009

    In case there are some smart biologists around, maybe someone can answer me this :

    The books will tell you that mutations in genes and genetic switches/non-coding segments etc alter the expression or proteins, break the protein expression, or create new variants etc etc…

    Now my question is, where and when does a mutation have to occur exactly, to be present in the next generation.
    What I mean is, obviously a mutation in my FOXP2 or whatever gene in one of my liver or glia cells occuring now makes no difference whatsoever for future generations,so it seems that a mutation not only has to be “the right one” to have effect X, but also only if it occurs in the right cell, at the right time.

    Maybe someone can explain that a bit.

  72. #72 Katrina
    December 31, 2009

    The show is now available at Nova’s website for those of us who didn’t/couldn’t watch it the first time, or for anyone who wishes to see it again.

    http://www.pbs.org/wgbh/nova/beta/evolution/darwin-never-knew.html

  73. #73 Yubal
    January 3, 2010

    # 68 David Marjanovi?

    Yeah, sure, but think of it like that, the DNA molecule has to be destroyed (e.g. Top1) for the replication machinery to work. I wouldn’t strictly separate both processes.

    # 71 Rorschach

    All cells in your body have the same information, the same DNA (more or less, there are cases of chimeras known where that is not true). The cellular expression of this information depends mostly on the tissue. The same gene can be expressed in proteins of several versions in different cell types. Therefore a mutation in one gene can be silent in one tissue but have severe effects in another one.

    How do mutations come in the next generation? Well, Sperm and egg. The mutation has to occur sometime between production of these gametes and the time the embryonic genome is assembled (or a little time after, like a mutation in the 8 cell stadium will give a mosaic chimera with 1/8 cells carrying a mutation and 7/8 do not.) to be present in the next generation. Take home message, there are stem cells in your body that produce those gametes. Their DNA is crucial for the next generation, and of course the processing during the subsequent gamete production, no system is error prone.

    The outcome of the mutation is absolutely not predictable. It has to be tested in the subsequent generation(s). In brief, everything that does something in your body is the result of a mutation that did occur at one point in time. Also, your offspring will have approx 150 random mutation compared to either you and your partner. Since these mutations usually do not matter the generation after them will carry them on until they really do something. A mutation that “suddenly” becomes “active” can be inside the genetic information for quite some time, like 100 generations or more. One example would be sweating glands of humans. We have more than monkeys do, probably because some hundred generations ago it was necessary to express more of them in order to be an efficient hunter. Maybe in 100 Generations humans will have much less sweat glands because body odor is nasty and only well-smelling subjects will be successful. Who knows? I don’t.

  74. #74 Kel, OM
    February 20, 2010

    Just watched the documentary, pretty cool apart from the first 30 minutes. I’ve got to say it made Evo-Devo seem such a cutting edge field of inquiry – no wonder PZ works in it. So many shiny graphics.

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