baudrunner's space: "criminal gene" report short on facts
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Tuesday, July 29, 2008

"criminal gene" report short on facts

The season finale of CSI:Miami on Monday night made reference to the presence of an extra Y chromosome in a suspect's DNA. Very little background information was provided about the double Y chromosome aberration, other than that it was stated that there was "no scientific evidence" that the presence of the extra Y chromosome made one more likely to demonstrate criminal behavior than the normal XY male.

The LA-based web site called cbs2, presumably an arm of the giant media conglomerate, corroborated this declaration with a column expressing very much the same opinion - that there was no evidence linking the double Y chromosome with a propensity for aggression or criminal behavior, and provided no more in the way of statistical or scientific data on individuals who possessed the extra Y chromosome than did the TV show.

However, I am certain that people want more than just a blanket declaration with no scientific evidence to back it up. Having read numerous volumes about the biology and physiology of the brain and having come across some interesting data during those readings and since, as our empirical knowledge grows ever greater on that subject I feel compelled to throw in my two cents with supporting links where I can, because, as it turns out, that blanket statement is not entirely correct, all factors considered.

The Y chromosome contains in the neighborhood of about 78 genes, or 86 genes, depending on the source of information. I have read that the Y chromosome contains about 150 genes, so it appears that the jury is out on the exact number but the differences may be accounted for by individual variations depending on the subject, although that is theoretical on my part. I have no other explanation for the discrepancies. In any case, these genes encode for about 23 proteins.

The X chromosome is considerably larger than the Y, but is considered to be gene- poor in scope because the largest segments of the DNA are thought to be non-coding portions. Depending on the source of information, the X chromosome contains anywhere from 900 to 2,000 or more genes. Therefore, anywhere from about four to ten percent of the genes in human DNA are found on the X chromosome. This great variance tells us that the state of the art in this type of genetic research is still somewhat primitive. On the other hand, it may also very well be that a significant degree of variation actually exists among different individuals.

In my article on this blog titled The ENCODE project: beyond the genome project it is revealed that large portions of what were once considered "junk DNA" are actually integral for the creation of the RNA templates which code for proteins. In fact, during transcription, many portions of different genes and non-genetic material distributed throughout the chromosome are combined to create the template. The functionality of the X chromosome is considerably greater than for the Y, which is essentially a sex-determinant gene and nothing more. There is recent evidence to support the idea that the X chromosome has more important reasons for being than merely for sex determination. It is known that the presence of an extra Y chromosome in about one in one thousand males "displaces" the X chromosome, rendering it ineffective.

Efforts to debunk a genetic link to aggression and violence abound. This makes sense from the legal point of view. Entering a "genetic predisposition to crime" defense should never be allowed because it throws the door open to the possibility of a genetic defense for any arbitrary situation. However, even the most scholarly articles have trouble convincing the reader that there is no basis for assuming that just because a male has an extra Y chromosome that he is at increased risk for running afoul of the law. The fact remains that it appears from a statistical standpoint that this is actually the case. Whereas the normal distribution of XYY males in the general population is about one in a thousand, a 1965 study of 196 dangerous criminals confined to a maximum security institution found eight XYY males. An unrelated Japanese study also found a disproportionate distribution of XYY males among its prison populations.

MRI studies of various aneuploidies of the sex chromosomes - XXX, XXY, XYY etc. - revealed reduced brain volume in all but the XYY karyotype. However, recent PET and MRI studies of XYY males showed negligible pre-frontal cortical activity. The study did not set out to study the XYY male, but rather to study brain activity under various conditions and stimuli. It was discovered that the entire brain is temporarily active when stimulated, just prior to concentrating the neural processing in dedicated areas like the occipital lobe or Wernicke's and Broca's regions, for example. When some subjects showed no neural activity in the pre-frontal cortex a DNA smear revealed the presence of the extra Y chromosome. Further studies of XYY males confirmed the absence of any significant neural processing in this region of the brain.

The pre-frontal cortex is the center of emotion and empathic reasoning, and, from Wikipedia: "This brain region has been implicated in planning complex cognitive behaviors, personality expression, and moderating correct social behavior." It is evident from the displacement of the X chromosome in XYY males, therefore, that much of the genetic content of the X chromosome is geared toward those attributes and functions. Also, since this is a rather large representative portion of the whole brain, it is little wonder then that the XYY male commonly develops learning disabilities as a child compared to the normal population. That alone would provide the impetus for possible anti-social behavior in the child's future if accommodations are not made in his upbringing.

Most XYY males lead normal lives, unaware that they possess an extra Y chromosome. It is therefore unwise to establish a genetic link to the predictability of a person's future behavior patterns. It is a fact that the greatest single influence determining whether a child becomes a criminal is still rooted in their upbringing and environment. Nevertheless, the claim that there is no scientific evidence to support the idea that an extra Y chromosome places the individual at higher risk for offending is obviously politically motivated. It is irresponsible, because it tends to mislead the student.

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