Notices
Results 1 to 11 of 11

Thread: endosymbiosis how does it get passed down the generations?

  1. #1 endosymbiosis how does it get passed down the generations? 
    Forum Freshman
    Join Date
    Jan 2011
    Posts
    90
    My first post here - pardon my ignorance. I am studying evolution but have no qualifications in biology only medical knowledge

    thinking of early plants and the fact that chloroplasts are integrated into their cells. How then do these plants ensure that:

    A) there are in fact a choroplast or tow in every cell?

    B) that chlorplasts get passed through any type of reproduction?

    C) in modern plans how to choroplasts get passed through seeds?
    given that they are not 'really' part of the plant and are a form of invasive bacteria

    D] Can any observations be made about mitochondria in Eukorytes in the same way?

    Zero


    Reply With Quote  
     

  2.  
     

  3. #2 Re: endosymbiosis how does it get passed down the generation 
    Forum Freshman
    Join Date
    Dec 2010
    Posts
    64
    Quote Originally Posted by ZeroZero
    A) there are in fact a choroplast or tow in every cell?

    B) that chlorplasts get passed through any type of reproduction?

    C) in modern plans how to choroplasts get passed through seeds?
    given that they are not 'really' part of the plant and are a form of invasive bacteria
    The same way they do with mitochondria.
    Both are descended from free bacteria, and reproduce within the cells (which have descended from archaebacteria).

    When a cell undergoes mitosis chloroplasts and mitochondria simply populate both haves of the splitting cell.

    Failure to do so would be strongly selected against for obvious reasons-on the levels of both the chloroplasts failing to inhabit environments, and the host cells themselves.

    Quote Originally Posted by ZeroZero
    D] Can any observations be made about mitochondria in Eukorytes in the same way?

    Zero
    Could you clarify?


    Reply With Quote  
     

  4. #3  
    Forum Freshman
    Join Date
    Jan 2011
    Posts
    90
    I think this has clear it up thanks - if meiosis is no different which would be the case I think

    cheers
    Reply With Quote  
     

  5. #4  
    Forum Professor Zwirko's Avatar
    Join Date
    Sep 2008
    Location
    55 N, 3 W
    Posts
    1,082
    It'd probably be best, and more correct, not to view plastids as "a form of invasive bacteria". They may have been free-living bacterial organisms some 1.5 billion years ago, but not now; today they are very much a part of the plant. If anything, the bacteria were more than likely engulfed rather than being invaders as such. Really though, rather than being "invasive" or being engulfed, it'd be better to view the original association as an endosymbiosis since its a two-way association.

    One particularly interesting thing is that most eukaryotes probably didn't in fact get their chloroplasts this way directly. Some early cells seem to have engulfed other cells that had already taken up what are now called chloroplasts; while yet other cells appear to have taken up those cells that had taken up the photosynthetic bacteria in the first instance. Primary, secondary and tertiary endosymbiosis.

    Another cools aspect of plastid biology is that most folks tend to associate chloroplasts with only plants, when in reality plants are just a sampling of the plastid-bearing eukaryotes out there. The malaria parasite (Plasmodium spp,) and Toxoplasma spp. have them too (not photosynthetic though). Technically known as apicoplasts, rather than as chloroplasts, it's not 100% clear what they do exactly.
    Reply With Quote  
     

  6. #5  
    Forum Freshman
    Join Date
    Jan 2011
    Posts
    90
    OK so if 1.4 b ago these cells invaded ours, or we engulved them, who is to say what else invaded and when? Is there anything else that passes the meoitic process and has seperate RNA/DNA?

    I am trying to understand what sort of grip speculations about the origin of life can get - how strong the claims are. I am not trying to dispute natural selection.

    Zero
    Reply With Quote  
     

  7. #6  
    Forum Professor Zwirko's Avatar
    Join Date
    Sep 2008
    Location
    55 N, 3 W
    Posts
    1,082
    The only other genome, besides those of certain viruses, plastids, mitochondria and their kin, that I know of are called "nucleomorphs" - which are really just remnants of the nuclear DNA of a eukaryote that was engulfed in a secondary symbiotic event.

    There are some hypotheses that attempt to explain the origin of the nucleus as arising from an endosymbiotic event(s) - including the idea that it is derived from an enveloped-DNA virus or from the plasma membranes of one or more bacteria.
    The cytoskeleton could perhaps be a blend of two cells that joined - one tubulin-based, the other actin-based. Indeed, the whole eukaryotic cell itself could be comprised of a mishmash of components arising from endosymbiotic and fusion events. As can be imagined, there are more hypotheses than there are hard facts at the moment.
    Reply With Quote  
     

  8. #7  
    Forum Freshman
    Join Date
    Jan 2011
    Posts
    90
    thank you for your replies Z.

    I am not a biologist but have some biology - my profession is psychiatry

    I am trying to determine which processes are involved in inheritence. I am trying to understand the central dogma and how/if Lamarkian inheritence of acquired characteristics - by the efforts of parents, is totally ruled out .

    Obviously the major process of inheritence is via the chromozones and meoisis and genes are passed on iusing crossover. Natural selection over the generations works its magic here.

    Mitochondria I understand has its own genes and is not involved in the crossover but is simply passed by replication in the egg and ovum? I assume there is still a possibility of mutation but adaptive mutation would take longer.

    There are also possibilities for other genomes ot pass from parents to child via virus and other bodies?

    Perhaps there are other mechanisms in addition to genes that are capable of passing data from parent to child? I would ont at this stage be able to speculate about what they were.

    I could not reach any conclusions but it seems to me that there is at least the possibility of bodies not involved in protien production, may have heriditory outcomes and should not be ruled out as mechanisms of forms of inheritence? At least without investigation.


    I am not sure if my biology is robust enough to assert this claim...



    Dawkins has a hard model which exclusively nominates genes as the mechanism of biological inheritence. I am tryng to verify how strong this claim is.

    (I still have not finished the Extended Phenotype and this may alter the view expressed in the Slefish Gene, BLind Watchmaker etc)


    Zero
    Reply With Quote  
     

  9. #8  
    Forum Professor Zwirko's Avatar
    Join Date
    Sep 2008
    Location
    55 N, 3 W
    Posts
    1,082
    First, lets clear up a few misunderstandings:

    1) The central dogma (in its more correct form) simply states that once the information encoded within a nucleic acid is transferred to protein, that information cannot flow backwards from protein to nucleic acid. That is, the final step in the flow of information from nucleic acid to protein is irreversible. It's a minor thing really, and not particularly relevant to what you are trying to understand.

    2) Mitochondrial DNA actually has a far higher mutation rate than nuclear DNA.


    3) The only genomes being passed to offspring in humans that you need concern yourself with are nuclear DNA and mitochondrial DNA, noting that the latter amounts to a just a tiny percentage of the total "information" that is passed on to the next generation. A rare exception occurs when some germ cells become infected with a retrovirus. When this happens the virus integrates a DNA copy of its genome into the nuclear DNA of a sperm or egg precursor cell. To be honest, I don't think you need concern yourself with this obscurity too much, except to know that it can happen.

    4) Genes don't always encode proteins. Many encode small RNA molecules of great biological importance; they are generally involved in regulatory roles. So, yes, you'd be right in stating that " the possibility of bodies not involved in protein production, may have hereditary outcomes and should not be ruled out as mechanisms of forms of inheritance".


    Perhaps there are other mechanisms in addition to genes that are capable of passing data from parent to child? I would ont at this stage be able to speculate about what they were.

    Genes and the chromosomes themselves can be chemically modified - in a sense "appending" an extra layer of "data" on to the gene. Such epigenetic modifications, while primarily a mechanism of gene control important in development, can also result in inherited changes in gene expression that do not arise from changes to the DNA sequence itself. Such changes have also been seen to occur in response to environmental exposure and transmitted from parent to offspring. This is about as close to Lamarckism as one dare go and still be on safe ground. It doesn't seem to be important on long time scales (i.e. evolution) as the changes tend to get reset after a while.

    On the theoretical side, some biologists like to raise the ghost of Lamarck from time to time in their speculations.
    Reply With Quote  
     

  10. #9  
    Forum Freshman
    Join Date
    Jan 2011
    Posts
    90
    thank you Zerko for cleaeing these matters up a little,

    It seems pretty clearn to me that I still have some misunderstandings to clear up about cell rreplicatiion both mitosis and meoisis.

    Can you recommend a good book or perhaps a link

    I have read a lot of Dawkins (some texts more than once), I have read The Origin, and understand basic biological terms (and organ functions etc) but want to understand genetics and cell structures more thoroughly.

    Intelligent layman text would be fine - I dont feel ready for research paper analyis yet I like pretty picvtures when it comes to visualising processes A really good childs text could be a start

    thanks

    Zero
    Reply With Quote  
     

  11. #10  
    Forum Professor Zwirko's Avatar
    Join Date
    Sep 2008
    Location
    55 N, 3 W
    Posts
    1,082
    An excellent starting resource is the obvious one: Wikipedia. Much maligned in the past, including by myself, Wikipedia has made great strides in both quality and depth in recent years and is now a great resource for learning the basics.

    The two articles "Biology" and "The Cell" are a great starting points. From these articles there is a wealth of links that lead ultimately to anywhere you want to go in the world of biology - several years of casual reading at least (with plenty of images). If you feel like toning down the level a bit then you can switch to the little-known Simple English Wikipedia version which drops a lot of the more confusing and technical aspects of many topics.

    A bunch of wiki articles is a bit more awkward to deal with than a nice good book I guess, but offhand I can't think of any decent books. Maybe someone else can...?
    Reply With Quote  
     

  12. #11  
    Forum Freshman
    Join Date
    Jan 2011
    Posts
    90
    Many thanks
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •