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.
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 However, I thought it wise to forewarn of this as it might possibly be outdated.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.