Trisomy…22?


Many people are familiar with Trisomy 21 in humans. Commonly known as Down Syndrome, Trisomy 21 severely affects human development via complex gene and environmental interactions. Genetically speaking, is this condition novel to humans? Or can this be seen in other primates? Most of the “great apes” contain 24 pairs of chromosomes, humans being the exception with 23. When compared, the two karyotypes  look strikingly similar. The only vast difference occurring on chromosome 2. From the diagram below, the human chromosome 21 and the great ape chromosome 22 look remarkably similar. Documented cases of Trisomy 22 in chimpanzees have been seen as far back as 1969. With the additional #22, symptoms parallel to Down Syndrome appeared.

 

C = Chimpanzee H = Human

 

So, this begs the question: how different are the chromosomes? In this article, the researchers set out to answer that. To do this, they used a probe from the human chromsome 21 (H21) that overlapped the “Down syndrome critical area” and placed it upon chromosome 22 of the great apes. Strangely, it worked! Homologous patterns for the H21 probe could be seen on chromosome 22 of all three of the remaining great apes. This indicates that the region associated with Down Syndrome is conserved phylogenetically.

*There are two issues of concern with this article. First, the figure detailing their work is completely blacked out in the article I was able to find (minor annoyance). Yet secondly, this paper was published in 1995 with my favorite part stating “the descent of human will continue to generate controversies in the evolutionary contest until the entire genome is sequenced.” *

Perhaps I shall write a follow-up on this topic if I am able to locate more recent literature. However, I thought it wise to forewarn of this as it might possibly be outdated. It’s still pretty cool though.

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About James R

A twice-over senior at the University of Minnesota - Morris. View all posts by James R

7 responses to “Trisomy…22?

  • Kevin Arhelger

    Thanks for hitting one of my pet peeves, you should use raises and not begs. It should read. “It raises the question: how different are the chromosomes?” Begging the question (petitio principii) is the logical fallacy of assuming the initial point. http://en.wikipedia.org/wiki/Begging_the_question

    An example
    1. Kevin is a troll.
    2. How do you know Kevin that?
    3. Because he is trolling.

    Oh, good work on your blog!

  • natural cynic

    …they used a probe from the human chromsome[sic] 21 (H21) that overlapped the “Down syndrome critical area” and placed it upon chromosome 22 of the great apes. Strangely, it worked! Homologous patterns for the H21 probe could be seen on chromosome 22 of all three of the remaining great apes. This indicates that the region associated with Down Syndrome is conserved phylogenetically.

    Why do you use the word strangely? It seems to me that if the characteristics of Trisomy22 in apes were similar to the characteristics of Trisomy21 in humans, that it would be odd if there were substantial differences in the comparable regions. It’s what would be expected with common descent

  • Peter

    I have a question about the fusing of chromosomes in human chromosome #2. I believe the fusion was between chromosomes 2 and 13. That would indicate that ape chromosomes from 14 to 24 would match human chromosomes 13 to 23. Is that what we see in the comparison of human and ape chromosomes?

  • Ctenotrish

    The difference with chromosome 2 really isn’t that vast … there was a chromosome fusion event somewhere between 740,000 and 3 million years ago. Basically, what are chromosomes 12 and 13 in chimps (non-human primates? I’d have to check) fused and became what we designate as chromosome 2 in humans. This is a good article if you have an interest in chromosome rearrangements in primate evolution. It’s some cool stuff! Kehrer-Sawatzki, H. and D.N. Cooper, Molecular mechanisms of chromosomal rearrangement during primate evolution. Chromosome Res, 2008. 16(1): p. 41-56.

    • James R

      Thanks for the article! The vast difference to which I was referring was along the lines of a visual comparison. In each pairing minor differences can be seen, but when compared to chromosome 2 and 12+13 (2 and the unmarked in the picture) they seem more pronounced. Otherwise, you’re completely correct. I was just going for a visual approach instead of genetic similarity. As for the “(non-human primates? I’d have to check)” I believe that applies only to the great apes. Although that is only an inference as that literature I read didn’t explicitly state otherwise.

  • Wayne Robinson

    Charles Darwin’s youngest child, Charles Waring Darwin, who died in 1858 aged less than 2, is thought to have had trisomy 21 (his death affected Charles Darwin greatly).

    The syndrome was only described in 1866, so it wouldn’t have been recognised at the time.

    There is a small percentage of individuals with trisomy 21, due to a balanced chromosomal translocation in one of the parents, who has 45 chromosomes. Conceivably, given a sufficiently large catastrophe and a lot of luck, humans could evolve to having 44 chromosomes instead of 46 (in the same way that humans originally evolved to 46 from 48). All you’d need is a pandemic that wipes out 99.99% of the human population leaving several very small surviving breeding populations, in which a few individuals with the 45 fused chromosome are present, and random neutral genetic drift will do the rest …

  • red rabbit

    I loved this research back in ’95. If I’m not mistaken, they have used cross-species primers to find homologies between genes in widely disparate species repeatedly since that time.

    Very cool stuff.

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