Tag Archives: genetics

Genetic Hybridization and Chronic Disease

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globalization-hands-picOver the Thanksgiving break, I was able to see a lot of my extended family that I really only get to see around the holiday season. I have a pretty large family so my Thanksgiving dinner included four generations—which creates a pretty large age gap between the oldest and most recent one. I am from the third generation so I try to interact across the entire lineage as much as possible. Through this, I have found out that my family (the Filipino side) has a history of high blood pressure and potential heart disease in the older generations. I had written a blog in the last blogging period about the benefits of genetic hybridization and whether or not it makes people stronger when it comes to battle diseases (also referred to as hybrid vigor). Because of the apparent link in race and some diseases (like in my family), I wanted to look at ethnic groups that don’t stray from within their own gene pool and see how that has affected their genetic development as a people.

 

During my research, the most information I found about hybrid vigor as it relates to chronic and prevalent diseases was on people form the Middle East. According to the US National Library of Medicine, a survey was done on breast and ovarian cancer rates depending on race and it was found that within the Middle East, Pakistanis has significantly higher rates than neighboring countries. The abstract stated that the cancer rate discrepancies couldn’t be explained with discrepancies of their risk factors. They proposed that observed cancer excess in Pakistan is due to cancer development by negative heterosis. Heterosis occurs when a hybrid has a phenotypic characteristic significantly different from that in either parent (hybrid vigor). The distribution of the survey were not stated which was one of my concerns because maybe there was some sort of gradient pattern of where this was most prevalent. There is the possibility that people closer to the center of the country had a higher frequency of the diseases compared to those closer to the border.

 

In a population, conditions that favor development of cancer by heterosis are those that favor mating of a large number of different homozygotes because they produce a large number of different heterozygotes. Among a large number of heterozygotes, there is an increased chance that some of hybrids will develop cancer by heterosis. In Pakistan, conditions were favorable for cancer development by heterosis because it has a high number of different ethnic groups and brotherhoods all of which have a higher rate of homozygosity due to a high frequency of consanguineous marriages (marriages between closely related people), and marriages between members of different groups occurred because of intense population mixing. Result was birth of a large number of inter-ethnic/brotherhood hybrids (heterozygotes), some of which have developed cancer by heterosis.

 

I found this information compelling but I didn’t want something that just done through a survey because of potential bias and the fact that it isn’t watching a progression and actively measuring something. After digging, I found a 5-year prospective study of 4934 children of different ethnic groups (which were not specified). The results showed that there was a three-fold increase of post neonatal mortality (between a month and a year old) and childhood morbidity in the offspring of consanguineous Pakistani parents.  It is estimated that 60% of the mortality and severe morbidity of this group of children could be eliminated if inbreeding ceased. I found this information extremely striking because of the shear magnitude of the possibility to overcome this issue. Looking at these two studies strengthens my previous argument about how being mixed with multiple ethic groups can be beneficial for one’s health—however looking at this culture the question of whether or not it is possible for some groups to actually branch out and mingle with other ethnic groups. The Middle East is a place that prides itself on culture and religion based on country and doesn’t look fondly upon intermingling so it might be hard for this issue to stop because of a cultural barrier, not a scientific one. So what does that mean from a global perspective? Personally, I think this is great news—it shows that some horrible and fatal diseases and issues have a potentially pretty simple solution if people allow it to happen. Having a realistic outlook on a future, I believe that though many diseases can be tempered with the increase of hybridization, we may potentially see other variations come up that we are not used to because of the new genetic combinations that are forming. But for now, I believe the pros outshine the cons and that hybridization not only help us physically, but also culturally and emotionally as we grow as a species.

 

 

http://www.ncbi.nlm.nih.gov/pubmed/15780500

http://europepmc.org/abstract/MED/8044647

Is Being Mixed Better Than Not?

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Our world is much different than it was just 50 years ago regarding dating and marriages. It has become more socially acceptable to date across races, which over time leads to a new generation littered with racially diverse children. This hits home for me because I am one of those children, my mother coming from the Philippines and my father from Jamaica, and my friends always thought it was so interesting that I was “exotic.” Personally, I did not think too much about it but I always wondered if my combination helped or hindered me in any health related way. It is believed that this trend of people with mixed races is going to only going to continue exponentially. National Geographic wrote an article describing the “Changing Faces” of America, and in the last 10 years the number of multiracial people has jumped by 32%, making it now one of the most popular categories(which was later reviewed by Time Magazine). So with all of this mixing going on, I had to ask myself—“Is being mixed better than not?” I read an overview of a documentary that aired on Channel 4—which is a British public-service television broadcaster—that tackled this question. You can watch the full documentary below.

All of the benefits from being mixed come first and foremost from the unique combinations within the genetic makeup. Everyone carries a handful of broken or malfunctioning genes that are only apparent when combined with another broken or malfunctioning gene. Similar broken genes can normally be found in areas where most of the people share the same racial profiles—so it is more likely than when two people with similar racial backgrounds come together that they will have a child with a weaker genetic makeup.

The term to describe an organism that has a higher growth rate and greater resistance to disease is “hybrid vigor”. Hybrid vigor can be divided into the components of outbreeding and heterozygote advantage. In essence, outbreeding leads to heterozygote advantage. As stated before, so-called “inbreeding”—or reproducing within your gene pool—can lead to serious physical deformities and health issues. Outbreeding pretty much scrambles the genes and make the chance that two malfunctioning genes will come together close to none.

So on the whole, mixed people seem genetically ‘better’. So, could mixed race children gain a noticeable genetic advantage and show degree of hybrid vigor? Some scientists think the answer is ‘yes’. However, as in other species, environmental conditions can mask the genetic effects, and in humans the environment can play an unusually big role. There are other cases of genetic hybrids outside of the human race—scientists had crossed animals and plants to analyze how they function as mixed entities. The differences between human populations are similar to if not greater than those seen between strains of plants and animals.

I think we need more time to watch how people develop as we continue to mix genes cross culturally. I agree with what National Geographic predicts, and I believe that we can potentially get to a point in time where there are more genetically diverse people than not (in short, no one will be “pure blood” any more).

http://content.time.com/time/health/article/0,8599,1880467,00.html

http://www.channel4.com/programmes/race-and-intelligence-sciences-last-taboo