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Old Nov 4, 2007, 07:13 pm   #57 (permalink) (top)
Athena
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Location: Oregon
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Well, I think to advance this discussion, we need some scientific information. Or we are ignorant people arguing opinions. Frankly, I am not that well informed. I just know the difference between ignorant opnions and basing arguments on facts. It takes a lot of energy to do the learning we need to do to have informed debates, and I don't have a lot of energy, nor the time to be well informed about everything we discuss. I know very little and often not enough to understand the facts I do find with the help of google, but if others want to put in the energy for the learning, I will too. It is like mountain climbing with experts who prepare before climbing a mountain, if people are truly well informed.

Quote:
Human and Ape Chromosomes

Creationists will be quick to point out that despite the similarities, there are differences in the chromosomal banding patterns and the number of chromosomes. Furthermore, they will claim that the similarities are due to a common designer rather than common ancestry. Let's address the differences first, and then we will see if we can tease apart the conflicting scenarios of common ancestry vs. a common designer.

The following observations can be made about similarities and differences among the four species. Except for differences in non genetic heterochromatin, chromosomes 6, 13, 19, 21, 22, and X have identical banding patterns in all four species. Chromosomes 3, 11, 14, 15, 18, 20, and Y look the same in three of the four species (those three being gorilla, chimps, and humans), and chromosomes 1, 2p, 2q, 5, 7 - 10, 12, and 16 are alike in two species. Chromosomes 4 and 17 are different among all 4 species.

Most of the chromosomal differences among the four species involve inversions - localities on the chromosome that have been inverted, or swapped end for end. This is a relatively common occurrence among many species, and has been documented in humans (Ref. 8 ). An inversion usually does not reduce fertility, as in the case I have referenced. Don Lindsay provides a diagram of the chromosome 5 inversion between chimpanzees and humans scanned from ref. 1. Note how all of the bands between the two chromosomes will line up perfectly if you flip the middle piece of either of the two chromosomes between the p14.I and q14.I marks. The similarity of the marks will include a match for position, number, and intensity (depth of staining). Similar rearrangements to this can explain all of the approximately 1000 non-heterochromatic bands observed among each of the four species for these three properties (band position, number, and intensity).

Other types of rearrangements include a few translocations (parts swapped among the chromosomes), and the presence or absence of nucleolar organizers. All of these differences are described in ref. 2 and can be observed to be occurring in modern populations.

The biggest single chromosomal rearrangement among the four species is the unique number of chromosomes (23 pairs) found in humans as opposed to the apes (24 pairs). Examining this difference will allow us to see some of the differences expected between common ancestry as opposed to a common designer and address the second creationist objection listed above.

There are two potential naturalistic explanations for the difference in chromosome numbers - either a fusion of two separate chromosomes occurred in the human line, or a fission of a chromosome occurred among the apes. The evidence favors a fusion event in the human line. One could imagine that the fusion is only an apparent artifact of the work of a designer or the work of nature (due to common ancestry). The common ancestry scenario presents two predictions. Since the chromosomes were apparently joined end to end, and the ends of chromosomes (called the telomere ) have a distinctive structure from the rest of the chromosome, there may be evidence of this structure in the middle of human chromosome 2 where the fusion apparently occurred. Also, since both of the chromosomes that hypothetically were fused had a centromere (the distinctive central part of the chromosome), we should see some evidence of two centromeres.


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