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Wednesday, May 20, 2009
Sunday, May 10, 2009
Some theories of Genitics
Vapour and Fluid Theories of Genetics
Early Greek philosophers speculated that the hereditary informations of parents existed in the form of vapours of fluids. Pythagoras (500 B. C.) speculated that a moist "vapour" descended from the brain, nerves and other body organs of the male during the coitus and from these vapours an embryo was formed in the uterus of the female. According to him, the male transmitted all the characters of the embryo and the female does not. However, another Greek philosopher of the same age, Empedocles thought that both parents contributed equally to the embryo and each parent produces a "semen" which arises directly from various body parts.
After 200 years, another Greek philosopher Aristotle forwarded a highly imaginative speculation that the seman of the male had certain 'vitalizing' or "dynamic" effect and it was supposed to be highly purified blood. According to him, the female furnished the inert building material, while the male gives the motion and new life to the material.
Particulate inheritance theory
The theory of particulate inheritance is an idea that originated with Mendelian theorists (or by Mendel himself) stating that characteristics can be passed from generation to generation through "discrete particles" (which meant genes). These particles can keep their ability to be expressed while not always appearing in descending generation.
Early in the 19th century, scientists had already recognized that Earth has been inhabited by living creatures for a very long time. On the other hand, they did not understand what mechanisms actually drove biological diversity. They also did not understand how physical traits are inherited from one generation to the next. Blending inheritance was the common ideal at the time, but was later discredited by the experiments of Gregor Mendel. Mendel proposed the theory of particulate inheritance by using pea plants (Pisum sativum) to explain how variation can be inherited and maintained over time.
Preformation theory
The Preformation theory states that "knowledge is possible only because God has endowed humans with certain innate ideas along with dispositions or aptitudes in certain ways." This was recognized by Immanuel Kant as an alternative to his theory regarding the categories of understanding and their source.
According to Kant's view the aptitudes are both innate and a priori not given by a creator. Contrary to Kant's position, the preformation theory avoids skepticism about the nature of the noumenal world (Kant believed that the real world is unknowable). It does so by claiming that the rational structures of the human mind are similar to the rational order of the real world because both are created by God to work together, and this similarity makes the attaining of accurate knowledge about the real world possible.
Germ plasm theory
Germ plasm or polar plasm is a zone found in the cytoplasm of the egg cells of some model organisms (such as Caenorhabditis elegans, Drosophila melanogaster, Xenopus laevis), which contains determinants that will give rise to the germ cell lineage. As the zygote undergoes mitotic divisions the germ plasm is ultimately restricted to a few cells of the embryo, these germ cells then migrate to the gonads.
The germ plasm theory is a hypothesis concerning the ability to become germ cells, which is now proven wrong. The term germ plasm was first used by the German biologist August Weismann (b.1834-d.1914) to describe a component of germ cells that he proposed were responsible for heredity, roughly equatable to our modern understanding of DNA. August Weismann formulated the now defunct germ plasm theory in 1893, in which he stated that the germ plasm was the essential nuclear part of germ cells, that it remained qualitatively unchanged from the zygote (in contrast with somatic cells) and was responsible for heredity. In other words it states that a gene's determination was sealed as it, and each of its offspring received fewer and fewer genes from what he called the "germ plasm." (That there is only a set "amount" of "germ plasm" (what we know as genes) and that it was gradually divided amongst the offspring). Cases such as Dolly (the famous cloned ewe) which, via somatic cell nuclear transfer, proved that adult cells retain a complete--as opposed to Weissman's increasingly determined gradual loss of genetic information--set of information; finally putting Weismann's theory to rest.
Early Greek philosophers speculated that the hereditary informations of parents existed in the form of vapours of fluids. Pythagoras (500 B. C.) speculated that a moist "vapour" descended from the brain, nerves and other body organs of the male during the coitus and from these vapours an embryo was formed in the uterus of the female. According to him, the male transmitted all the characters of the embryo and the female does not. However, another Greek philosopher of the same age, Empedocles thought that both parents contributed equally to the embryo and each parent produces a "semen" which arises directly from various body parts.
After 200 years, another Greek philosopher Aristotle forwarded a highly imaginative speculation that the seman of the male had certain 'vitalizing' or "dynamic" effect and it was supposed to be highly purified blood. According to him, the female furnished the inert building material, while the male gives the motion and new life to the material.
Particulate inheritance theory
The theory of particulate inheritance is an idea that originated with Mendelian theorists (or by Mendel himself) stating that characteristics can be passed from generation to generation through "discrete particles" (which meant genes). These particles can keep their ability to be expressed while not always appearing in descending generation.
Early in the 19th century, scientists had already recognized that Earth has been inhabited by living creatures for a very long time. On the other hand, they did not understand what mechanisms actually drove biological diversity. They also did not understand how physical traits are inherited from one generation to the next. Blending inheritance was the common ideal at the time, but was later discredited by the experiments of Gregor Mendel. Mendel proposed the theory of particulate inheritance by using pea plants (Pisum sativum) to explain how variation can be inherited and maintained over time.
Preformation theory
The Preformation theory states that "knowledge is possible only because God has endowed humans with certain innate ideas along with dispositions or aptitudes in certain ways." This was recognized by Immanuel Kant as an alternative to his theory regarding the categories of understanding and their source.
According to Kant's view the aptitudes are both innate and a priori not given by a creator. Contrary to Kant's position, the preformation theory avoids skepticism about the nature of the noumenal world (Kant believed that the real world is unknowable). It does so by claiming that the rational structures of the human mind are similar to the rational order of the real world because both are created by God to work together, and this similarity makes the attaining of accurate knowledge about the real world possible.
Germ plasm theory
Germ plasm or polar plasm is a zone found in the cytoplasm of the egg cells of some model organisms (such as Caenorhabditis elegans, Drosophila melanogaster, Xenopus laevis), which contains determinants that will give rise to the germ cell lineage. As the zygote undergoes mitotic divisions the germ plasm is ultimately restricted to a few cells of the embryo, these germ cells then migrate to the gonads.
The germ plasm theory is a hypothesis concerning the ability to become germ cells, which is now proven wrong. The term germ plasm was first used by the German biologist August Weismann (b.1834-d.1914) to describe a component of germ cells that he proposed were responsible for heredity, roughly equatable to our modern understanding of DNA. August Weismann formulated the now defunct germ plasm theory in 1893, in which he stated that the germ plasm was the essential nuclear part of germ cells, that it remained qualitatively unchanged from the zygote (in contrast with somatic cells) and was responsible for heredity. In other words it states that a gene's determination was sealed as it, and each of its offspring received fewer and fewer genes from what he called the "germ plasm." (That there is only a set "amount" of "germ plasm" (what we know as genes) and that it was gradually divided amongst the offspring). Cases such as Dolly (the famous cloned ewe) which, via somatic cell nuclear transfer, proved that adult cells retain a complete--as opposed to Weissman's increasingly determined gradual loss of genetic information--set of information; finally putting Weismann's theory to rest.
Wednesday, May 6, 2009
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