mercredi 7 janvier 2015

Telocentric Chromosomes of Rhinoceros, check ... Rock Wallaby, check ...

Here is a model, which I have been attacking, giving the word to Peter Borger (link below signature):

In 1970, Neil Todd developed the karyotypic fission hypothesis (KFH)* to correlate the physical appearance of chromosomes with the evolutionary history of mammals. Todd postulated wholesale fission of all medio-centric chromosomes. Todd’s fast-track, single event, genome rearrangement still is the most parsimonious theory to account for mammalian karyotypes and potentially explains rapid speciation events. Todd’s was rejected mainly because it postulated something opposing the dominant Darwinian paradigm.

In 1999, Robin Kolnicki revived Todd’s KFH. Although her kinetochore reproduction hypothesis** was largely theoretical, each step had a known cellular or molecular mechanism. During DNA replication, just before meiotic synapsis and sister chromatid segregation, the formation of an extra kinetochore on all chromosomes is facilitated. The kinetochore is the organizing centre that holds the sister chromatids together during meioses and is composed mainly of repetitive DNA sequences. The freshly added kinetochores do not disrupt the distribution of chromosomes to daughter cells during meiosis because tension-sensitive checkpoints operate to prevent errors in chromosome segregation. The result is a new cell with twice the number of telocentric chromosomes.***

The duplication of the kinetochores on many chromosomes at the same time is highly unlikely in a naturalistic model, but the telocentric chromosomes of rhinoceros, rock wallaby and many other species are physical evidence that their genomes were formed instantly. [My emphasis.]

Notes * Todd, N.B., Karyotypic fissioning and canid phylogeny. J. Theor. Biol. 26:445–480, 1970.

** Kolnicki, R.L., Kinetochore reproduction in animal evolution: cell biological explanation of karyotypic fission theory, Proc. Natl Acad. Sci. USA, 97:9493–9497, 2000.

*** Koonin, E.V., The Biological Big Bang model for the major transitions in evolution, Biology Direct 2:21, 2007

Here is the specific claim of evidence: but the telocentric chromosomes of rhinoceros, rock wallaby and many other species are physical evidence that their genomes were formed instantly.

If by instantly you mean by special creation, no problem.

But if by "instantly" you mean by an event instantaneous in the sense of "karyotypic fission hypothesis" whether as a single event or otherwise, I do not see how this is evidenced by "telocentric chromosomes of rhinoceros" UNLESS the word telocentric here means strictly telocentric, i e such where one of the telomeres is also working as a centromere, or where a centromere while retaining its work of holding the two chromsome strings together also is a telomere, furnishing the outer protection of genome strands so these do not unravel because of precisely lack of such protection. The male Y chromsome is such a strictly telocentric chromosome, its one telomere is also a centromere and attaches to the centromere of the X chromosome (you cannot live without X chromosome, and if you have two of them you are a woman).

  • Is such strict telocentric arrangement what we find in rhinoceroi?

    No. Not only at least and I do not know how much even. Unfortunately for the clear discussion of the issue, very acrocentric chromosomes, such where you find little or no genome string between one telomere and the centromere are ALSO called "telocentric". A somewhat better terminology is "subtelocentric" - it makes it sound like the centric mere is sub/under the telo one. This is what you find in rhinoceroi:

    In 10 blood metaphase plates the chromosome number was 84. The group of subtelo- and submetacentric autosomes seemed to include 9-16 pairs of chromosomes with one or two small and nearly metacentric pairs (Fig. 1, pair M). The other pairs of autosomes were all acro- or telocentric. The X chromosome was the longest submetacentric chromosome of the karyotype (q/p = 1.7), and for that reason it was easy to distinguish, even by conventional Giemsa staining. The Y chromosome was not identified.

    From : Hansen, K.M., 1976. Q-bands of some chromosomes of the white rhinoceros (Diceros simus). Hereditas 82: 205-208, fig. 1, table 1

    In other words, even if some telocentric pairs of autosomes (non-sex chromosomes, where a pair is by one chromosome and "this" [auton] same-type from other parent, unlike sex-chromosomes, where pairs of at least one sex are by one chrosome pairing with a clearly OTHER [unlike]), even if some such do occur - and we do not know how many since the salient fact for the interest of Hansen was just counting "submetacentric" (nearly but not quite middle position of centromere) and "subtelocentric" (telomere just outside centromere on one of its sides), not to distinguish between acrocentric (where centromere is clearly closer to one telomere than to other) and telocentric (where there is identity of element between one telomere and the centromere) - there are also others.

    If ALL had been telocentric, strictly, well, then a fair guess might have been there might just have been a karyotypic fission - at least if it is to be explained as I have seen it explained in P. Z. Myers. The problem is that all aren't. Hansen for rhinoceros counts the subtelocentric and submetacentric ones and forgets to distinguish which ones of the rest are acrocentric (non-products of fission) and which ones are strictly telocentric (possible products of fission).

    Note, a metacentric or submetacentric chromosome could theoretically be produced by fusion of two fission products that did not belong to same previous usually acrocentric chromosome. But here we would be dealing with two events, a fission event and a fusion event.

  • So, rock wallaby ...

    The two karyotypes differ significantly from the plesiomorphic karyotype of the genus and from those of all other Petrogale species examined. Petrogale brachyotis and P. concinna are characterised by three synapomorphies: a 1-10 centric fusion, a 3a-6 centric fusion, and a submetacentric chromosome 2 (2s). Both species also possess autapomorphies. Petrogale brachyotis is characterised by submetacentric chromosomes 5 (5s) and 4 (4sm), whereas P. concinna is characterised by a 5-9 centric fusion and a submetacentric chromosome 8 (8m). The 2s, 5s, 4sm, and 8m chromosomes all appear to be derived from their plesiomorphic homologs by centromeric transpositions.

    From Abstract from : Cytogenet Cell Genet. 1992;61(1):34-9.
    Chromosomal rearrangements in rock wallabies, Petrogale (Marsupialia: Macropodidae). VII. G-banding analysis of Petrogale brachyotis and P. concinna: species with dramatically altered karyotypes.
    by Eldridge MD1, Johnston PG, Lowry PS.

    Note we have not one example of "fission" and not one example of strictly telocentric chromosome mentioned. The submetacentric ones could each be a trace of two former telocentric ones, but we do not see any such in this abstract. Of course, I could be so very wrong about strictly telocentric chromosomes once we get to the full text - but I don't have it.

    Fusion is not the problem. I had initially thought fusion was as problematic as fission, because it gives rise to a generation where one part of genome sequence is in one chromosome held together from new fusion from one parent and in two chromosomes attached to it from the other parent giving a normal karyotype half.

    No, fission is more problematic, unless immediate results are strictly telocentric, like Y chromosomes and possible ulterior results are metacentric or submetacentric, but this latter does not make the chromosome number higher than it started out as.

  • "and many other species"

    Unfortunately that is not clear as to which ones.

Back to Borger on CMI:

I postulate that the genomes, as we observe them today, are the result of thousands of years of rearrangements (fission, fusion and duplications) brought about by specific variation-inducing genetic elements (VIGEs). Initially, well controlled rearrangements may have been facilitated by these elements, but over time the control over regulated genome rearrangement deteriorated. VIGEs may be the genetic basis to help us understand wholesale genomic rearrangements from pluripotent baranomes.

Well, fusion happens. Hares and rabbits can have a common ancestor - if the common ancestor had the chromosome nulber which is higher of the two. But not if the common ancestor had the chromosome number which is lower of the two.

I could be wrong to say fission NEVER happens, but I have as yet been offered no evidence it has. And such evidence would include such strictly telocentric chromosomes that are rare, and if they were not, how come I have not been offered a clear example? Either case, they are NOT the main staple of karytype variation in mammals. And this sets a severe limit on how low the first mammals can have been as to chromosome number. Similar restrictions do not apply so that God could not create similar kinds, different from beginning and never to mix, which differ precisely most clearly in karyotype. The observation is one about a naturalistic process of "fission". Against it.

Hans Georg Lundahl
Nanterre UL
Ember Wednesday of Epiphany-Tide,
as I recall?

PS, I think of those who celebrate Christmas day today, according to Julian rather than Greforian Calendar, wishing all the best!/HGL

CMI : Evidence for the design of life: part 2—Baranomes
by Peter Borger

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