PSY307-X-chromosome hypothesis
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Section 1
The X chromosome is one of the sex determining chromosomes. The letter “X” was assigned to this chromosome for being such a unique gene. Both male and female mammals carry an X chromosome, two X chromosomes for females and one for males. Current research on the X chromosome shows that aggression is not directly linked to each other. Although, it does suggest that sex chromosomes may play a part in feelings and actions of aggression, the significance of it is not substantial.
Unfortunately, for X chromosome hypothesis, there was little to no information regarding this topic. However, my understanding of the unique gene, the X chromosome, is that it’s contained in both male and female. Consequently, any possible examples that I may present can derive from me looking at the women in my life and those that surround me at the office or in school; and then examining the amount they carry and have on their plates that come from work, school and home. When I watch the news at night and see women who have aggressed towards a person or sometimes their own offspring. I wonder if maybe all that aggression or built stress derive from the fact that we have two X chromosomes or is it that just like anyone else they have reached their breaking point and went “off the deep end”. Although, this is all hypothetical, it is a question that has many possible answers but also it’s a question that has been tested and the results do not directly point to the X chromosome.
An article in Science Daily, written in 2006, suggests that the Y chromosome has more of an effect on aggression. The article also suggests that the X chromosome is directly linked to a maternal component (University, 2006). The experiment conducted in this article, consisted of mice both with and without the Sry gene, which is a gene found on the Y chromosome found in males, in comparison with XX versus XY chromosomal mice. The study was conducted to test how long it took the mice to become aggressive. This was tested by seeing the reaction of the mice when another mouse crosses into their territory. The results showed that the mice with Sry with either XX (female mice who were injected with Sry) or XY were found to be aggressive. However, the female mice with the XX complement were not aggressive.
The study, Aggressive and Mating Behaviors in Two Types of Sex Reversed Mice: XY Females and XX Males, authors Canastar, Maxson and Bishop, conduct a study testing aggression in both male and female mice, just like the study discussed previously. The subjects consisted of XY males and XX and XY, injected with Sry, females. The procedure was similar to the one previously discussed, in that they put each mouse in their own quarters (home), and an intruder was placed in their by the experimenter. The male mice were shown to be more aggressive in the first experiment. Although, the males carried both sex chromosomes, X and Y, the relation between the X chromosome and aggression is not shown. This is because the female mice, both the XX and the injected Sry mice, did not exhibit any signs of aggression (Canastar, Maxson, and Bishop, 2008).
In the study, Sex Chromosome Complement and Gonadal Sex Influence Aggressive and Parental Behaviors in Mice, it is suggested that using the same technique as the other studies (mice and intrusion of other mice, also adding soiled bedding to the factor), that XX mice took longer to show signs of aggression as opposed to the female mice with X and Y, injected chromosome. Also in this study the bearing of the pups was apparent in female mice. Moreover, the Sry gene being of independence for the female mice may be the reason for their constant maternal actions.
However, in an article about monoamine oxidase (MAO), it is suggested that this gene, both the A and B element are located on the X chromosome. In the article, they propose that, “MAO A knock-out mice have elevated brain levels of serotonin, norephinephrine, and dopamine and manifest aggressive behavior similar to human males with a deletion of MAO A” (Shih, Chen, and Ridd, 1999). In humans as well as mice and other rodents, MAO A appears before MAO B in most tissues in the body. MAO B knock-out in mice did not show a significant amount of aggression. In addition, aggressive behavior is also found to be present in children with Fragile X syndrome. This syndrome occurs when a specific gene on X chromosome is altered (Fragile). Most or the time when this occurs in girls, it is much more subdued than when it occurs in boys. Due to the fact that girls carry two X chromosomes and the one that it is not affected can compensate for the one that is.
The research conducted in the articles and the example of a possibility of aggression does not match up; however, it helps to subtract hypotheses out the equation; the X chromosome is shown not to be directly correlated with aggression. Nevertheless, the Sry gene in both XX and XY mice shown signs of aggression, but the Sry gene is a gene that is found in males. Therefore, the injection of Sry gene was the reason for aggressive actions in the XX mice and not because of natural reasons, per se.
Section 4
The Columbine shooting that occurred back in 1999, still lingers with whispers of “Why?” and “How did we not see this coming?” But the complete understanding of it may never surface because only two people who are no longer here know the complete story. Eric Harris and Dylan Klebold were classmates at the Colorado high school, Harris who the media suggests to be a psychopath and Klebold who, at the time, was dealing with depression. Depression is something that has been known to affect women more so than men. If this is indeed a fact, then one could propose that because women are statistically diagnosed more often with Depression, it may possible be correlated with the X chromosome (being that females carry both the X chromosomes), and a son would receive his X chromosome from his mother, this possibility could definitely be entertained.
Unfortunately, that would only cover a minimal of the cause of why the two young men would have aggressed towards those individuals in their high school. The X chromosome does not seem to carry much relevance in this case (only the possibility discussed previously). Neither could the X chromosome have been used to prevent this type of aggression and violence. However, since many of the research shows that much aggression derives from the Y chromosome, one could possibly say that if the X chromosome was more dominant maybe this massacre would have never happened. Unfortunately, even with the research and how it stands, there is still no concrete evidence that this would be true.
References:
Canastar, Andrew, Maxson, Stephen C., and Bishop, Colin, E. (2008). Aggressive and Mating Behaviors in Two Types of Sex Reversed Mice: XY Females and XX Males. Archives of Sexual Behavior Journal. 37, 2 – 8.
Chen, Stephanie. (2009). Debunking the myths of Columbine, 10 Years Later. Cable News Network. http://www.cnn.com/2009/CRIME/04/20/columbine.myths/
Gatewood, Jessica D., Wills, Aileen, Shetty, Savera, Xu, Jun, Arnold, Arthur P., Burgoyne, Paul S., and Rissman, Emilie F. (2006). Sex Chromosome Complement and Gonadal Sex Influence Aggressive and Parental Behaviors in Mice. The Journal of Neuroscience. 26 (8), 2335 – 2342.
Shih, J.C., Chen, K., and Ridd, M. J. (1999). Monoamine Oxidase from Genes to Behavior. Annual Review of Neuroscience. 22, 197 – 217.
The American Heritage Dictionary of the English Language, Fourth Edition (2009). Houghton Mifflin Company. http://dictionary.reference.com/
Fragile X Syndrome. The ARC of Georgia. http://parenttoparentofga.org
University of Virginia Health System (2006). Sex Chromosome Genes Influence Aggression And Maternal Behavior, Say Researchers. Science Daily. Retrieved May 19, 2009, from http://www.sciencedaily.com¬ /releases/2006/03/060306214707.htm
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