Introduction to Genetics: A Molecular Approach - site edition by Terry Brown. Download it once and read it on your site device, PC, phones or tablets. Genetics today is inexorably focused on DNA. The theme of Introduction to Genetics: A Molecular Approach is therefore the progression from molecules ( DNA. introduction to genetics a molecular approach terry brown pdf free download.
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This approach to the study of genetics is often referred to as classical ge- netics, or organismic or morphological ge- netics. Given the advances of molecular, or. The text explains the basic principles of molecular biology and genetics and is ideal for modern introductory courses in these subjects. The book begins by. Historical development of the chromosome theory. The nature of Detecting human disease alleles: molecular genetic diagnostics. Genetic.
Inheritance of Genes in Bacteria Inheritance of Genes during Virus Infection Cycles Inheritance of Genes during Eukaryotic Sexual Reproduction Mutation and DNA Repair Genes in Differentiation and Development The Human Genome Genes in Industry and Agriculture Weber adopts a mixed theory of refence.
According to mixed theories, the reference of a term is determined how the relevant linguistic community causally interacts with potential referents as well as how they describe potential referents.
This theory leads Weber to pay close attention, not just to how geneticists theorized about genes or used the concept to explain phenomena, but also how they conducted their laboratory investigations. Following Kitcher , , he examines ways in which modes of reference changed over time. Weber identifies six different gene concepts, beginning with Darwin's pangene concept and ending with the contemporary concept of molecular genetics.
Weber examines how the investigation of several particular Drosophila genes changed as the science of genetics developed. His study shows that the methods of molecular genetics provided new ways to identify genes that were first identified by classical techniques.
An Introduction to the Genetics and Molecular Biology of the Yeast Saccharomyces cerevisiae
The reference of the term changed, not simply as a result of theoretical developments, but also as a result of the implementation of new methods to identify genes.
She says that in this context, interest in genes is largely focused on the regulated expression of polypeptides.
She notes that textbook definitions of gene often acknowledge this interest and quotes the following definition from a scientific textbook: A combination of DNA segments that together constitute an expressible unit, expression leading the formation of one or more specific functional gene products that may lead to either RNA molecules or polypeptides.
The segments of a gene include 1 the transcribed unit … and any regulatory segments included in the transcription unit, and 2 the regulatory sequences that flank the trancription unit and are required for specific expression.
Singer and Berg , p. Neumann-Held points out that if the aim is to specify what is necessary for regulated synthesis of polypeptides, then one must include even more than what is located in the DNA.
This follows from the fact that processes such as differential splicing and RNA editing processes such as methylation that I have not discussed in this article involve entities outside of DNA such as splicing agents. She suggests that it is appropriate, at least in the context of developmental genetics, to reconceive genes as processes. She proposes the following process molecular gene concept. The term gene in this sense stands for processes which are specified by 1 the specific interactions between specific DNA segments and specific non-DNA located entities, 2 specific processing mechanisms of resulting mRNA's in interactions with additional non-DNA located entities.
Neumann-Held , p. Neumann-Held's concept excludes transcription processes and coding regions of DNA that lead to functional RNA molecules that are not translated into polypeptides. This feature of Neumann-Held's definition does not match the textbook definition that she quotes to motivate her account presented above. Furthermore, the exclusion of these coding regions does not track with recent discoveries about the important functions played by non-coding RNA molecules such as snRNAs.
Her definition could easily be revised to accommodate these regions and processes.
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They point out that individual philosophers cannot grasp all the intricacies of the different contexts across the broad range of biological sciences in which gene concepts are employed. They have embarked upon an ambitious project to survey practicing scientists in an attempt to help identify how scientists actually conceive of genes.
An initial motivation behind Stotz and Griffith's project was to test philosophical accounts of the gene concept. As Griffiths asked, if their survey-based study revealed that scientists don't actually think of genes in the way set out by a philosophical account, then what value could the account possibly have?
It is also difficult to survey appropriate and representative samples of scientists. Griffiths and Stotz are aware of these difficulties and have refined their project through successive surveys.
Even if Stotz and Griffith's survey succeeds in identifying how scientists in different areas of biology actually think about genes in different contexts, it does not follow that their findings would provide an appropriate test of the classical, molecular, or process molecular gene concepts. The aim of the proponents of these concepts is to re-interpret the knowledge of contemporary genetics by replacing sloppy thinking based on unclear concepts with more rigorous thinking in terms of precise concepts.
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Showing that scientists' actual thinking does not align with the precise application of these concepts would not refute the analysis supporting the classical gene or molecular gene concepts and it would not undermine the argument motivating the proposal for the new process molecular gene concept. Although it appears that survey-based findings would not provide an appropriate test of philosophical analyses of gene concepts, they might provide, as Stotz and Griffiths claim, important information relevant to those conducting philosophical research on gene concepts.
For example, if such surveys find significant differences in the way evolutionary biologists and developmental geneticists answer questions about what counts as gene, philosophers might examine whether the contexts in which these biologists practice call for different gene concepts. Survey results could provide a useful heuristic for conducting concept analyses. They argue that the term is both too vague and too restrictive.
It is too vague, they believe, because it does not provide a unique parsing of the genome. Borders between genes are overlapping and allegedly ambiguous. It is not clear, they argue, whether genes include or exclude introns, regulatory regions, and so forth. The term is allegedly too restrictive because it obscures the diversity of molecular elements playing different roles in the expression and regulation of DNA. In addition, any attempt to resolve the ambiguities, these skeptics argue, will make the term even more restrictive.
Keller's account of the history of twentieth century genetics seems to reinforce gene skepticism. For example, she argues that the question about what genes are for has become increasingly difficult to answer Keller By the end of the twentieth century, she says, biological findings have revealed a complexity of developmental dynamics that make it impossible to conceive of genes as distinct causal agents in development.
Keller , p. Keller identifies a second reason that gene talk is useful. The term gene applies to entities that can be experimentally manipulated to produce definite and reproducible effects though given Keller's criticism of gene concepts, it is unclear to what entities she thinks the term refers.
She suggests that genes are short-term causes. She points out, however, that this does not mean genes are long-term causes or that genes are the fundamental causal agents of development. Rather, what it means and Keller thinks this is an important reason why gene talk will continue is that genes can be used as handles to manipulate biological processes also see Waters And for these two reasons, Keller concludes, gene talk will and should continue to play an important role in biological discourse.
What do genes and DNA do? The science called molecular genetics is associated with a fundamental theory according to which genes and DNA direct all basic life processes by providing the information specifying the development and functioning of organisms.
The information of development and function, which is passed down from one generation to the next, is allegedly encoded in the nucleotide sequences comprising genes and DNA. By the early s, the language of information was well-entrenched in the field of molecular genetics.
Critics have taken a number of different positions. Most seem to accept the notion that biological systems or processes contain information, but they deny the idea that DNA has a exceptional role in providing information.
Some are content to argue that under various existing theories of information, such as causal theories or standard teleosemantic theories, information is not restricted to DNA. But others contend that understanding what genes do requires a new conception of biological information.
One approach is to retreat to a narrow conception of coding specifically aimed at clarifying the sense in which DNA provides information for the synthesis of polypeptides, but not for higher-level traits e. Godfrey-Smith Another approach is to construct a new, broad conception of biological information and use this conception to show that the informational role of genes is not exclusive Jablonka A different approach is to abandon information talk altogether and explain the investigative and explanatory reasoning associated with genetics and molecular biology in purely causal terms.
Keller points out that the idea flounders on an ambiguity. Oyama suggests that it is a mistake to think information is contained within static entities such as DNA. She believes that information exists in life-cycles. Other criticisms challenge applications of particular conceptions or theories of information, including applications of the causal and teleosemantic conceptions. Griffiths distinguishes between two ways to conceive of information, causal and intentional, and then argues that under either conception, information is not restricted to DNA.
Causal theories of information, based on Dretske's , are related to the Shannon mathematical theory of information Dretske distinguishes between a source variable and background or channel conditions. On Griffiths' reading of Dretske's theory, a source variable, X, carries information about variable Y if the value of X is correlated with the value of Y. Griffiths describes the causal interpretation of this idea as follows: There is a channel between two systems when the state of one is systematically causally related to the other, so that the state of the sender can be discovered by observing the state of the receiver.
The causal information is simply the state of affairs with which it reliably correlates at the other end of the channel. Thus, smoke carries information about fire and disease phenotypes carry information about disease genes. Griffiths , p. It follows that genes carry information about phenotypes because phenotypic values reliably correlate with genotypic values.
But as Griffiths points out, nothing stops one from treating environmental conditions as source variables and genes as channel.
Under this application of the causal theory, environmental conditions carry information about phenotypes. Griffiths and others have concluded that the idea that genes provide the information while other causal factors merely provide material cannot be sustained under causal theories of information. Griffiths argues that the idea that genes and DNA provide all the information fares no better under intentional theories of information.
The version of intentional theory favored by philosophers of biology is teleosemantic. According to teleosemantic theories, a signal represents whatever it was selected to represent in the process of evolution.
Under this idea, one might say that DNA contains information about development because DNA's effects on development were selected for in the process of evolution. But as Griffiths and Gray point out, this idea applies to a wide range of entities involved in development, not just DNA. Weber challenges Maynard Smith's teleosemantic account. Maynard Smith draws an analogy between information in a programmed computer and information in DNA.
Computers execute algorithms programmed by human beings and organisms express DNA that has been programmed by natural selection. The information programmed in a computer is intentional in that one could determine the intentions of the human programmer by analyzing the algorithm. Maynard Smith argues that the information programmed in DNA by natural selection is intentional in the same sense.
Weber offers two arguments against this view. First, he points out that DNA might contain nucleotide sequences that have arisen from chance mutations that happen to be beneficial. If natural selection has not yet operated on them, then Maynard Smith's teleosemantic theory implies they do not contain information.
Yet, causally, such a nucleotide sequence would influence development in the same way as sequences that have been selected for. Weber's second criticism of Maynard Smith's account stems from a closer examination of the intentionality associated with computer programs. Weber claims that intentional states associated with computers are actually states of the human engineers who write the programs, not states of the computers themselves: "A computer program is a string of symbols that acquires a meaning only in the context of a community of engineers who understand what the program does and what it can be used for" Weber , p.
The analogue to human programmers in Maynard Smith's account is natural selection.
But natural selection does not have intentional states. Hence, Weber concludes, the teleosemantic approach fails to save the idea that DNA contains information in the intentional sense. It is tempting to think that information talk is impotent in this context and indeed, some philosophers have argued that such talk is misleading and should be abandoned e.
But others have taken the view that more careful thinking about concepts of information could lead to important insights see next section. One of her concerns is that discussions about the meaning or non-meaning of information talk in biology are biased by the assumption that the genetic system should serve as the prototype for thinking about biological information. She believes that a general definition of information, one designed to capture the senses of information exemplified in environmental cues, man-made instructions, and evolved biological signals, as well as the sense of information in hereditary material, will lead to more useful generalizations and perspectives.
Jablonka says that the sense of information in all these situations involve a source, a receiver system organism or organism-designed system , and a special type of reaction of the receiver to the source.
She conceives the receiver's reaction as a complex, regulated chain of events leading to a response. Variations in the form of the source lead to variations in response. That is, the nature of the reaction depends on the way the source is organized. In addition, she points out, reactions in these situations are beneficial for the receiver over an appropriate period of time in the case of organisms, over evolutionary time. Jablonka stresses that the benefit, or function, in the case of organisms should be understood in terms of evolution, with the focus on the evolution of the reaction system, not on the evolution of the source or the evolution of the final outcome of the reaction.
Jablonka's concept of information is intentional, and is related to the teleosemantic conceptions discussed above.
According to standard teleosemantic conceptions, signals have information because the production of the signal was selected for in evolutionary history.
According to Jablonka's view, however, an entity has information, not because it was selected for, but because the receiver's response to it was selected for. Whether something counts as information depends on whether entities respond to it in a proper functional way.
Jablonka summarizes her general account in the following definition: A source — an entity or process — can be said to have information when a receiver system reacts to this source in a special way. The reaction of the receiver to the source has to be such that the reaction can actually or potentially change the state of the receiver in a usually functional manner. Moreover, there must be a consistent relation between variations in the form of the source and the corresponding changes in the receiver.
Jablonka , p. Jablonka argues that the information in DNA has little in common with the information in an alarm call, a cloudy sky, or a chemical signal in a bacterial colony. But in the case of DNA, the receiver does not seem to react in a way that adapts the cell to anything in particular.
Nevertheless, Jablonka claims that her concept applies to genes even if it doesn't apply to DNA in general: However, if instead of thinking about DNA in general we think about a particular locus with a particular allele, it is not difficult to think about the functional role of this particular allele in a particular set of environmental circumstances. Hence we can say for all types of information, including alarm calls and pieces of DNA, a source S allele, alarm call, cloudy sky, etc.
Jablonka's orignal account provides an illuminating way to think about information in biological processes such as cellular signaling processes. But her account does not substantiate the idea that genes and DNA contain information or help elucidate the role of genes and DNA. This approach is premised on the idea that the basic theory and laboratory methods associated with molecular genetics can be understood in purely causal terms.
The basic theory and methodology concerns the syntheses of DNA, RNA, and polypeptide molecules, not the alleged role of DNA in "programming" or "directing" development section 2. The causal role of molecular genes in the syntheses of these molecules can be understood in terms of causally specific actual difference making.
This involves two causal concepts, actual difference making and causal specificity. These concepts can be explicated in terms of the manipulability account of causation. The concept of actual difference making applies in the context of an actual population containing entities that actually differ with respect to some property.
In such a population, there might be many potential difference makers. That is, there may be many factors that could be manipulated to alter the relevant property of the entities in the population. But the actual difference makers are roughly speaking the potential difference makers that actual differ, and whose actual differences bring about the actual differences in the property in the population.
The concept of actual difference making can be illustrated with the difference principle of classical genetics section 2. According to this principle, genes can be difference makers with respect to phenotypic differences in particular genetic and environmental contexts.
So, it identifies potential difference makers. When this principle is used to explain an actual hereditary pattern, it is applied to genes that actually differed in the population exhibiting the pattern often an experimental population. In such cases, an actual difference in the gene among the organisms in the population caused the actual phenotypic differences in that population see Gifford That is, the gene was the actual difference maker, not just a potential difference maker in that population.
The concept of actual difference making can be applied to molecular genetics as follows. In an actual cell, where a population of unprocessed RNA molecules differ with respect to linear sequence, the question arises: what causes these differences? The answer is that differences in genes in the cell cause the actual differences in the linear sequences in the unprocessed RNA molecules, and also in populations of RNA molecules and polypeptides.
Genes are not the only actual difference makers of the actual differences in the linear sequences of these molecules.
Genetics: A Molecular Approach
And this brings us to the second causal concept, causal specificity. Causal specificity has been analyzed by Lewis The basic idea is that a causal relationship between two properties is specific when many different values in a causal property bring about many different and specifically different values of a resultant variable the causal relationships instantiate something like a mathematical function. A dimmer switch is causally specific in this sense.
Genes can be specific difference makers because many specific differences in the sequences of nucleotides in DNA result in specific differences in RNA molecules. Biologists have discovered, however, the existence of other actual difference makers, besides genes and DNA, that are causally specific with respect to the linear sequences of processed RNA and polypeptides, to some degree at least.
For example, in some cells splicing complexes called splicosomes actually differ in multiple ways that result in multiple, specific differences in the linear sequences of processed RNA molecules. The fact that all kinds of entities are causally relevant to the synthesis of RNA might lead one to think there is causal parity among the causal elements.
But this account shows that genes and DNA play a distinctive causal role in that genes are the causally specific actual difference makers of difference in the linear sequences of unprocessed RNA molecules. This distinctive role extends with important qualifications to the linear sequences of processed RNA molecules and polypeptides.
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A Brown is a pastor of 40 years. He's written twelve books, including First There Was Fire. He holds a B. He has been bi-vocational throughout his career, having worked as a carpenter, surveyor, EMT, and fire fighter. Books by T. Trivia About Genetics:A male and female bird have 4 unhatched eggs.
Genes S and T are not linked. Yet red is a very complex color, requiring the interaction of at least five and probably of very many more different genes for its production. When the process is complete, two copies of the original double helix have been formed and hence the genes in the original DNA molecule have been effectively replicated.
Download with Google Download with Facebook or download with email Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.
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