How Do Changes in Chromosome Number Evolve - Term Paper Example

How do changes in chromosome number evolve?" Evolution is the progression of alteration and modification in all aspects of life over creation. The bio-assortment of life progresses through natural selection, mutations and genetic drift. It is established that every individual carries a plethora of genetic material or genes inherited from the previous generation and then passes this genetic material to the next generation. Observations reveal that offspring display some kind of variation from their parents, owing to the genetic manipulation that cells undergo during the process of cell division. In certain cases these variations lay the foundation of evolution of chromosomes and variation in their numbers. Introduction The process of evolution is solely based on the genetic manipulation encompassing natural selection where the nature shows favouritism for some organism over the other resulting in the domination of their offspring displaying higher level of robustness. Genetic characters are responsible for natural selection and superior adaptation of the organisms, this is one of the major reasons that pave the way for evolution and therefore organisms are not precisely alike over the generations. Evolution is more persistent if the populace becomes secluded either all the way through ecological or geological distance or by methods that check genetic swapping. Eventually, secluded population can diverge into novel species (Gould, 2002). Another method of evolution is genetic drift, these drifts are the resultant of slight mutations in genes, causing changes in chromosomes. In many cases mutations do not bring any remarkable changes and do not even cause any injury to the organism. Survival of these modified genes in the organism cause genetic alterations and are passed to the next generation. These genetic changes could be seen in the phenotype of the organism where alterations are obvious and measurable. Such changes differ from the natural selection process which is responsible for acting on only the adaptation mandatory for the survival of the organism (Garvin-Doxas, 2008). These two alteration process are continuous processes. Species are constantly evolving, this can be seen when a comparison is drafted between the inhabitants on the planet when the life began around 1 billion years ago and the present organisms. Evolution is the resultant of chromosomal alteration was approved by Darwins principle of natural selection and thereby laid the foundation of every aspect of modern ordinance of science encompassing agriculture, medicine and drugs, physiology, biology or forensic science. According to Darwins theory of natural selection, rivalry for the available resources do occur between inter species as well as between intraspecies. This holds true in todays world this holds true in every sense of competing world including human survival. Those who survive the competition are the fittest ones and hence the resultant of the competition is survival of fittest (Wyhe, 2002). Modern era of evolution is based on Darwins theory of natural selection, it is postulated that these variation in certain cases are genetic or chromosomal and therefore they are inherited. On the other hand the concern is these alterations should be in the genital cells producing gametes while the alterations in the somatic cells cannot be transmitted to the next generation. In contrast to the Darwins theory Lamarckism postulated the inheritance of acquired characters and hence use of certain organ and disuse of other could eventually lead to the modification or disappearance of the organ respectively (Bejder, 2002). G. J Mendel, laid the basis of the inheritance. His experiments with pea plant demonstrated that genes are the basic units of heredity in all living organisms. Information about the genotype and phenotype of the organism is stored in these genes. Later it was revealed that genes are made up of De-oxy-ribonucleic acid or DNA, DNA contains four nitrogen bases, Adenine, Guanine, Cytosine and Thymine. It is the combination of these nitrogen bases and their sequential arrangement, which dictates the phenotype and genotype of the organism. The genes are intact in the chromosome which are present in the nucleus of the cell. The trundling of the genes present in the chromosomes aids in the new permutation and combination eventually resulting in the evolution of the organism. Mutations are sudden abrupt changes that occur in the genes. Alteration in single nitrogen base present in the DNA could result in the change of the entire meaning that was carried by that gene. DNA a double stranded genetic material forms single stranded RNA by the process of transcription. RNA in turn forms the protein responsible for various regulatory mechanisms involved in the metabolism of the organism. Alteration occurring at any one step can potentially alters the entire protein synthesis thereby leading to the formation of wrong protein or cessation of protein synthesis. This may display serious consequences and rarely result in favour of the organism. If this mutation occurs in any vital protein synthesis process then it may be fatal but if it occurs in a protein or in gene which may lead to the formation of a protein which is responsible for playing crucial role in the adaptation of the organism it results in evolution of that species. In present era, bacterial population show resistance towards various drugs, this resistance is attributed to the alteration in the genes of the cells which are developed gradually over the time. It is obvious that bacterial cell possess single chromosome and is prokaryotic with ill-defined nucleus and absence of cell organelles. In case of strains resistant for certain drugs another extra-chromosomal DNA is reported called the plasmid. Thus bacterial cell possess two chromosomes, the second one being small and carries resistance factors. It is also established that species do possess fixed number and set of chromosomes. For e.g. Drosophila melanogaster possess four pairs of chromosomes while human beings possess 23 pairs of chromosomes. One factor that could form the basis of this comparison is, humans are more evolved and therefore they possess more number of chromosomes than Drosophila. It is also observed that earthworms possess more chromosomes than humans also some of the animals do possess more number of chromosomes than humans indicating that there could not be any relation between the number of chromosomes and the genetic superiority. It is also observed that mutation must happen in both the set of chromosomes that are inherited from both the parents for evolution, any kind of impairing between the two or more sets of chromosomes leads to polyploidy. In the process of cell division the chromosomes segregate and hence each cell retains the same number of chromosomes as the parent. In case of non-disjunction of chromosomes during the process of cell division, duplication of gene occur. This non-disjunction could be due to any kind of mutagenic agent capable of causing mutation in the chromosome. These extra chromosome leads to redundancy in the metabolism of the organism or may undergo an evolution enabling gene to perform any special function. Promoters of Darwin state that gene duplication serves as a foundation of new meaning of genes, while the other set of genes take the responsibility of performing normal course. It is evident that bacterial cell possess single set of chromosome along with plasmids. It is also established that life originated in water from the primordial soup, it is therefore probable that the principle of duplication might have worked during the course of evolution. According to Ernst Mayr, Darwinists of the 20th century, "Such a new gene is called a paralogous gene. At first, it will have the same function as its sister gene. However, it will usually evolve by having its own mutations and in due time it may acquire functions that differ from those of its sister gene. The original gene, however, will also evolve, and such direct descendants of the original gene are called orthologous genes" (Mayr, 2001). According to Ohno, gene duplication is the process that produces new gene, Ohno further states that the evolution from bacteria to human is attributed to the duplication of genes as well as the duplication of whole genomes, this is responsible for the enormous jump in evolution. Evolution from invertebrates to vertebrates could be accredited to the process of duplication (Li, 1997). According to Kellis, "whole-genome duplication followed by massive gene loss and specialization has long been postulated as a powerful mechanism of evolutionary innovation" (Kellis, 2004). Thus evolution by the process of duplication is due to exaptation; a supposed evolutionary progression where an arrangement advanced for some other reason is reassigned to its existing task (Goffeau, 2004). It is manifested that gene duplication occur in nature. These duplications are in terms of gene duplication, chromosome duplication or duplication of entire set of chromosomes. It is essential to understand the process of duplication not only to understand the process of evolution but also for the complete understanding of numerous diseases as every metabolic alteration is associated with the gene and could turn fatal. According to Li, polyploidy could result in the disproportion of gene product. Novelty in gene occur when duplication is within limits. In humans trisomy of 21st chromosome is the resultant of non-disjunction of chromosomes during the anaphase of the cell division. This is called Downs syndrome. Thus duplication of gene causes the abnormal condition. Chromosome duplication is also observed in plants where polyploidy is highly widespread phenomenon. In plants polyploidy augments cell size reducing the cell surface-volume ration thereby condenses some cellular functions, alters metabolism and growth of the plant. On the other hand some of the polyploids show resistance to drought, pest and other pathogen attack and any kind of mineral deficiency in the soil (Levin, 2002). Most of the insects also display polyploidy. Male bees are haploid (n) while females are diploid (2n), indicating that males do not evolve at faster pace. Duplication of gene is sufficient to afford an enough foundation for development? A study conducted by Lynch and Conery used steady-state demographic methodologies to correctly establish the amount of duplicate genes. They concluded that ‘the average rate of duplication of a eukaryotic gene to be on the order of 0.01/gene/million years, which is of the same order of magnitude as the mutation rate per nucleotide site’(Lynch, Conery, 2003). The above arguments present a picture that gene duplication does occur and it may have laid the foundation of evolution and changes in the chromosome causing variation in the number of chromosomes in eukaryotic population. Duplication of chromosome forms the firm basis to illustrate the fact related to the variation in the chromosomes amongst the inhabitants of the earth. Chromosome duplication can be useful in plants and invertebrates but in case of vertebrates gene duplication do not form the firm basis of the argument that chromosome number and variation in chromosome number between different animal species is solely attributed to the process of chromosome duplication. Although Darwin and its supporters emphasize that gene duplication is imperative for the evolution as they could not form any other basis of chromosome number variation apart from duplication process (Pennisi,, 2001). Inheritance of the features that has made the species survive could form basis to the changes in the chromosomes. There is always a possibility of genetic variations within a population of individuals. It is observed that a particular group of organisms display some features that enable them to survive even the tough environmental situations making them more adaptable to the adversity over their peers. These adaptations could be in the form of phenotype or there is a possibility that variations might have taken place in thr form of genetic mutation leading to the synthesis of protein that made them more versatile and adaptable. It is therefore essential to postulate the role of environment on deciphering the number and kind of chromosomes leading to the evolution of the organism. These features are inherited by the offspring and if the offspring fail to inherit the traits then it leads to the extinction of the species. It is evident that evolution is a gradual process and nothing has taken place over night. It took more than 1 billion years to shape the present epoch of life. On the other hand mutation has played its role by bringing random variation in the species. It is therefore essential to understand that the product of evolution can never be to procure a perfect organism as evolution is a continuous process. The result is merely an individual capable of surviving in a superior manner and also able to reproduce more effectively than its competitors in that fastidious environment. On studying the evolution tree it was postulated that there is some kind of common ancestry that is shared between the plants and animals. This is also proved by means of fossils and redundancy of the genetic code, the DNA, the RNA are also universal molecules which are present throughout the living world. There are several divergence in the evolution tree that demonstrate the presence or absence of some genetic traits that lead to the evolution of new organism with different set of chromosomes and thereby displaying difference in the phenotype of the organisms. It is also evident that there is some kind of co-relation that exist as human brain is correlated to the shape of walnut and also chambers in tomato is related to the chambers of heart but these are completely non-related tissues, although walnut is good for brain development and tomato for heart health. Tracing down the ancestry genes have descended much before but some reminiscent are still present although there is a variation in the chromosome number, variation in the expression of genes but they seem to have evolved from the common ancestors. Thus various correlations can be traced out which enumerate the reasons of variation in the chromosome numbers and their development. Expression pattern of the genes, their environment, the kind of protein they synthesize and the kind of environment they are activated in. All these cumulatively lead to the variation in the chromosome number, pattern the kind of gene they predispose and the role they play in the synthesis of protein formation. Conclusion Life originated on the planet form a single cell that were called co-acervates and to the recent data which displays the number of chromosomes to be 64 as reported in horse. This is solely attributed to the ability of the DNA molecule to replicate, this is a small molecule that forms the basis of chromosomes. This serves as the basis of formation of various organisms. It is the arrangement of genes in these chromosomes that pave the way for any organisms to be what they are. Probably a non-disjunction of chromosomes after replication leads to a new kind of cell which on further replication forms a set of novel chromosome matter of the cell. Assimilation of these chromosomes would have formulated a new kind of organism. Tracing back the history of evolution, viruses are the entities which are supposed to be the connecting link between the living a and non-living things. These viruses also carry the genetic material DNA or RNA but never the both, they very proficiently utilize the host cell machinery for their replication, this virus also has the potential to become dormant by incorporating with the host cell DNA. Probably in the past epochs the incorporation of this viral genetic material into the host cell chromosome would have lead to the configuration of a new kind of protein. As proteins are the building blocks of the cell so this protein would have resulted in the formation of keratin and has lead to the formation of hair in a few organisms like mammals. Also, similar situations might have taken place when bacteria attack the host cell with a few plasmids and chromosomal material. Incorporation of these genetic material in the cellular or host chromosome would have resulted in some kind of mutation leading to the formation of new-fangled chromosomes. These chromosomes might have carried the information of innovative protein which had given rise to a new organism. Mutations due to climatic changes, weather, environmental hazards also pave the way for the formation of novel organisms. It is believed that no two organisms on this planet are exactly alike. Further strengthening the argument that it is not only the genotype of the organism but its phenotype also that plays the imperative role in devising the organism to the new form. The geographical distribution on the planet varies and so the organisms also varies from place to place, these are all due to the various kinds of adaptations that they have undergone over the centuries to make themselves suit to the environment and their surroundings. A camel has padded feet to walk on the desert, moreover it has hump to survive in the desert. All these alterations are due to the chromosomal evolution that has made the animal to suit the Darwins theory of Survival of the fittest. Understanding also says that changes in the chromosomes might not have taken place in the entire population but only a few would have exhibited such changes leading to the changes in the genetic make-up of the organism and hence such changes could be passed on to the future generations. The flora and fauna of the geographical area displays the information of the geography of that particular area of the planet. It directly implies that to suit to the surroundings of this area, organisms have modified themselves to a greater extent and only the meaningful variations and changes could be entertained by the nature, these changes carry meaning as they can be passed on to the next generations so that they can thrive on that particular geographical distribution of nature. Those organisms, remain incapable to modify their chromosomes or genes by the process of recombination of DNA, shuffling of chromosomes and production of a meaningful modification were lost and were taken over by those who could generate and accomplish such changes. The story of evolution therefore is solely dependent on the chromosomal alterations which the organisms have gone through by means of various gene manipulation methods which are now-a-days being exploited by the molecular biologists to generate medicines and drugs for dreaded diseases. Development of resistance in the microorganisms is a direct implication of the fact that chromosomes or DNA or RNA are constantly undergoing evolution to adapt themselves to the competitive environment and thereby constantly throwing challenges to the scientist for the development of more innovative drugs. In the present era people talk about "Super Human" which is also going to be the sole contribution of the evolution in the chromosomal biology. Thus, evolution of chromosome, in the terms of number, the distribution of genes, the pattern and kind of protein being synthesized, the kind and extent of adaptation to changes or modifications taking place in the environment is solely attributed to the genetic manipulation and various kinds of chromosomal combinations that occur during the cell division and growth. References Bejder, L., Hall, B. K. (2002). Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss. Evol. Dev. 4 (6): 445–58. Bergman, J. Does gene duplication provide the engine for evolution. Available at http://creation.com/does-gene-duplication-provide-the-engine-for-evolution [Accessed on 30th October 2010] Goffeau, A. (2004). Evolutionary genomics: seeing double, Nature 430:25. Gould, S. J. (2002). The Structure of Evolutionary Theory. Harvard University Press. pp. 1433. Kellis, M., Birren, B.W., Lander, E.S. (2004) Proof and evolutionary analysis of ancient genome duplication in the yeast Saccharomyces Cerevisiae, Nature 428:617–624. Levin, D.A. (2002). The Role of Chromosomal Change in Plant Evolution, Oxford University Press, NY, p.134. Li, W.-H. (1997). Molecular Evolution, Sinauer Associates, Sunderland, MA, p. 269. Lynch, M., Conery, J.S. (2003). The evolutionary demography of duplicate genes, J. Structural and Functional Genomics 3:35–44. Mayr, E. (2001). What Evolution Is, Basic Books, NY, pp. 108–109. Pennisi, E. (2001). Genome duplications: the stuff of evolution? Science 294:2458–2460. Wyhe, John van (2002). "Fertilisation of Orchids". The Complete Works of Charles Darwin. University of Cambridge. http://darwin-online.org.uk/EditorialIntroductions/Freeman_FertilisationofOrchids.html Read More