As you may already know, the origins of many of the features on the human head, such as the jaws, ears, larynx, and throat, can be traced to the gill arches from an embryo to an adult in a human. If look back to the Handy Genes chapter, a similar phenomenon occurs when the origin of the wing of a chicken can be trace to a wing bud and areas close to the ZPA, where high concentration of ZPA molecule exist, develop the wing in the exact way they are supposed to. I noticed a pattern. Almost all the features that organisms develop originate from a tiny region of cells, much like the entire embryo originates from a single ball of cells called the morula. My question is whether this is significant to understanding evolution, and whether this phenomenon occurs across multiple species (and kingdoms) to explain the source of changes that brought about speciation and diversity.
Consider the theme of evolution. Almost all organisms originate as tiny cells and develop from such minute beginnings into the organisms they are destined to become, but why is that so? Could this be a weak spot for earth dwelling organisms because “if anything interferes with normal development during the embryonic phase, the effects can be devastating.” (Weiten, 427). Is this important period of development the very period during which diversity comes to be?
Weiten, W., & Halpern, D. (2004). Motivation and Emotion. Psychology: Themes and Variation 6th Edition, 10, 427
Troy Glickstern
The development of organisms from tiny cells to much larger, more complex multicellular organisms has benefits and disadvantages. Since organisms today feature this type of development, it's logical to assume that evolution has favored this method.
ReplyDeleteThe benefits of this type of development include simple concerns like the size of the developing organism and more complex concerns like energy usage. In mammals, for instance, a pregnancy would be impractical if the unborn organism were somehow as large as its parent. Furthermore, the organism expanding and thereby using more energy before it is developmentally able to differentiate its new cells would be wasteful.
The real reason, though, that animals specifically have to originate from one cell and develop into many is that the fusion of a sperm cell and an egg cell to create a zygote is the start of the new life form (Campbell 1013). Evolution has favored sexual reproduction for its ability to create change in a population, so animals (which reproduce sexually) have to develop from tiny cells.
Developmental issues are negative, but less important, effects of this type of growth. Even though developmental diseases, like cerebral palsy, for instance, can cause effects like hindered motor skills, these relatively rare effects are not significant enough to overcome the benefits of this development (http://www.cdc.gov/ncbddd/dd/ddcp.htm).
The real, important aspect of conception is the fusion of sperm and egg to produce DNA unique from that of each parent, which has been favored by evolution.
- Vincent Fiorentini
(vincent@panatechcomputer.com)
While it is natural to believe that the mutations while being at the root of the evolution also results in many developemental diseases, one cannot help but to wonder if there is natural selection process at work, then why is there such a high rate of genetic disorders? or why does mutation happen at all? One of the most common and frequent developemental disease in a certain area is the Huntington's Chorea. This disease is caused by the dominant allele which means that if one is carrying this gene, he or she will show phenotypic symptoms of this disease. Based on the human genome research, scientists determined that the repeated codon CAG results in the contraction of this disease. Considering all the genes in our DNA and different possible mutations, it almost seems as if the risk of mutation is greater than its benefit from evolutionary standpoint. It is even believed that this disease was responsible for eliminating nearly half of a village in Venezuela.(http://evolution.berkeley.edu/evolibrary/article/_0_0/medicine_05)
ReplyDeleteMany scientists have asked what made these genetic disorders and other possible dangers to persist in the developement of fetus. Vincent in the above post mentions that the meeting of sperms and eggs provide evolutionary advantage by creating diversity within a given population through mutation and yes that may be an almost perfect answer as to why mutation and other dangers of developement persisted. However, although sad as it seems, based on recent research, scientists argued that because we all evolved from a common ancestor, the faults of that ancestor still persists throughout its evolutionary history almost as if it was the ultimate weakness of all earth dwelling organisms. Although this may seem dark, it also brings a new light of hope. Unlike diseases caused by another organisms, which often involves coevolution, where mutation causes continual variation causing an evolutionary arms race, developemental defects or diseases reulting from mutations tends to be static throughout evolutionary history. With the advent of Human Genome Project, scientists, through phylostratigraphy, were able to trace through the evolutionary history of genes. The findings baffled the scientists. By tracing the genes, they discoevered that most of the genes responsible for the genetic disorders existed in one of the very first cells. Furthermore, scientists discovered that despite the advent of the mammal, no new genetic disorders appeared. (http://www.sciencedaily.com/releases/2008/10/081016124043.htm) Scientists further concluded that one of the latest genetic disorder came about 400 million years with the advent of the bony fish. If the genetic disorders were already present in the first cell, then how is it that some genetic disease only happen to certain animals while not effecting others? This almost hints that the muatation unlike what has traditionally been believed may have some organized system in the way its conducted. Unfortunately, the mutation's randomness still stands. However, the answer to the question can be answered by the transcriptional phase of gene regulation. The reason why certain mutations may show phenotypic effects in some species while not in other lies in the fact that throughout life, majority of the genes are "turned off" or not transcripted into RNA than made into protein. However, one question still unanswered even to scientists (as far as I looked into) is that many of the recently evolved genes that are active in mammals doesn't result in genetic disorder or show phenotypic signs of the mutation present in the gene.(http://www.sciencedaily.com/releases/2008/10/081016124043.htm)
Kevin Jeon
bboybyung@gmail.com