Artists, poets and musicians play with palindromes all the time. They mirror images, reverse words, invert musical phrases — yet cleverly manage to retain the original meaning. “A man, a plan, a canal, Panama” is a favorite palindrome that reads the same backward as it does forward. We have palindromes in our bodies, too — in the way DNA will sometimes encode information. The results are a little bit different, and in fact, have recently been found to cause disease.
The case of the disappearing genes
The X and Y chromosomes started out with about the same number of genes — around 1,000. Yet, today, the Y chromosome has less than 80 genes. Why is that? Part of the answer is that it doesn’t have a partner to swap genes with, a mechanism to keep the good genes and repair bad ones. Will the Y chromosome keep getting smaller and eventually disappear? Six years ago, David Page, Director of the Whitehead Institute, asked that question.
The palindrome solution
Dr. Page found that while it continues to lose genes, it has been secretly making backup copies of the most important ones. The copies are in 8 large areas of mirror-image ATCG sequences on the chromosome. The Y folds itself in the middle of these palindrome regions, allowing the genes to pair and fix areas damaged by random mutations. More on this in a minute.
Curious folding hairpin shapes
As an artist, I’m intrigued by shape and movement and how that plays out in our DNA. I brought my sketch pad and questions to an expert — Professor Perry Hackett, geneticist at the University of Minnesota. As we talked about the curious story of the shrinking Y, Perry sketched two strands of DNA splitting apart and recombining into a shape known as a hairpin. The new structure is a palindrome and he explained that folding and shape changing behavior is common at the molecular level. Our genome is dynamic.
Beware the reflect tool
All the reversing and folding and flipping got me thinking about how often artists use this kind of symmetry in their work. MC Escher comes to mind with his repetitive, reflected shapes that brilliantly create new forms in negative space. Escher would have loved a digital tool I use in Adobe Illustrator called the “reflecting tool”. (The icon for it is shown below). Beware ill considered use, though! Inverting a photo, especially of someone you know, makes them look not quite right. Duplicating a human hand in that way leaves out the nuanced differences — making the image less rich.
Shortcuts in art and in nature — not always a good plan
In the September 2011 issue of Cell, Dr. Page has follow up research to his discovery of the Y chromosome palindrome sequences. The Y’s process of recombination sometimes turns the entire chromosome into a palindrome. With two centromeres the Y gets its signals crossed and can lead to…. well, crossing over. The abnormal structure is connected to a range of sex disorders: low sperm count, Turner Syndrome and in some cases, sex reversal. The good news is that scientists now understand the genetic mechanism, so courses for treatment can be developed.
About the images shown above
The colorful graphic at the top was designed for my show at the Bell Museum. The white circle shows a man’s X and Y chromosomes under the microscope. The graphic with the yellow stripes is a stylized image of the Y chromosome and the blue band is the sex determining SRY gene. Below the graphic are sketches by Professor Perry Hackett. The hand drawings are mine with the small symbol for the reflect tool between them. The MC Escher example is also an illustrated version of a tessellation, a mathematical term. The image on the bottom is a precise example of a DNA palindrome by the artist Toska, courtesy of Wikimedia commons.