Principles Of Genetic

[Elenio Guardado]

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Cells navigate environments, communicate and build complex patterns by initiating gene expression in response to specific signals. Engineers seek to harness this capability to program cells to perform tasks or create chemicals and materials that match the complexity seen in nature. This Review describes new tools that aid the construction of genetic circuits. Circuit dynamics can be influenced by the choice of regulators and changed with expression 'tuning knobs'. We collate the failure modes encountered when assembling circuits, quantify their impact on performance and review mitigation efforts. Finally, we discuss the constraints that arise from circuits having to operate within a living cell. Collectively, better tools, well-characterized parts and a comprehensive understanding of how to compose circuits are leading to a breakthrough in the ability to program living cells for advanced applications, from living therapeutics to the atomic manufacturing of functional materials.

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Abstract: Genetic engineering is the use of molecular biology technology to modify DNA sequence(s) in genomes, using a variety of approaches. For example, homologous recombination can be used to target specific sequences in mouse embryonic stem (ES) cell genomes or other cultured cells, but it is cumbersome, poorly efficient, and relies on drug positive/negative selection in cell culture for success. Other routinely applied methods include random integration of DNA after direct transfection (microinjection), transposon-mediated DNA insertion, or DNA insertion mediated by viral vectors for the production of transgenic mice and rats. Random integration of DNA occurs more frequently than homologous recombination, but has numerous drawbacks, despite its efficiency. The most elegant and effective method is technology based on guided endonucleases, because these can target specific DNA sequences. Since the advent of clustered regularly interspaced short palindromic repeats or CRISPR/Cas9 technology, endonuclease-mediated gene targeting has become the most widely applied method to engineer genomes, supplanting the use of zinc finger nucleases, transcription activator-like effector nucleases, and meganucleases. Future improvements in CRISPR/Cas9 gene editing may be achieved by increasing the efficiency of homology-directed repair. Here, we describe principles of genetic engineering and detail: (1) how common elements of current technologies include the need for a chromosome break to occur, (2) the use of specific and sensitive genotyping assays to detect altered genomes, and (3) delivery modalities that impact characterization of gene modifications. In summary, while some principles of genetic engineering remain steadfast, others change as technologies are ever-evolving and continue to revolutionize research in many fields. Keywords: CRISPR/Cas9; embryonic stem (ES) cells; genetic engineering; gene targeting; homologous recombination; microinjection; retroviruses; transgenic mice; transgenic rats; transposons; vectors

Each new genetic test that is developed raises serious issues for medicine, public health, and social policy regarding the circumstances under which the test should be used, how the test is implemented, and what uses are made of its results. Should people be allowed to choose or refuse the test, or should it be mandatory, as newborn screening is in some states? Should people be able to control access to the results of their tests? If test results are released to third parties such as employers or insurers, what protections should be in place to ensure that people are not treated unfairly because of their genotype?

The answers to these questions depend in part on the significance given to four important ethical and legal principles: autonomy, confidentiality, privacy, and equity. A review of the meaning of those concepts and how they are currently protected by the law provides a starting point for the development of recommendations on the degree of control people should have in deciding whether to undergo genetic testing and what uses should be made of the results. The task is a pressing one. In a 1992 national probability survey of the public, sponsored by the March of Dimes, 38 percent of respondents said that new types of genetic testing should be stopped altogether until the privacy issues are settled.1

This chapter reviews some of the conflicts that will arise in the research and clinical settings, and suggests general principles that should be the starting point for policy analyses in this evolving field.

Autonomy can be defined as self-determination, self-rule, or self-governance. Autonomous agents or actions presuppose some capacity of reasoning, deciding, and willing. Moral, social, and legal norms establish obligations to respect autonomous agents and their choices. Respect for personal autonomy implies that agents have the right or power to be self-governing and self-directing, without outside control. In the context of genetic testing and screening, respect for autonomy refers to the right of persons to make an informed, independent judgment about whether they wish to be tested and then whether they wish to know the details of the outcome of the testing. Autonomy is also the right of the individual to control his or her destiny, with or without reliance on genetic information, and to avoid interference by others with important life decisions, whether these are based on genetic information or other factors. Respect for autonomy also implies the right of persons to control the future use of genetic material submitted for analysis for a specific purpose (including when the genetic material itself and the information derived from that material may be stored for future analysis, such as in a DNA bank or registry file).

Even though respect for autonomy is centrally important in our society, it is not absolute. It can be overridden in some circumstances, for example, to prevent serious harm to others, as is the case in mandatory newborn screening for phenylketonuria (PKU) and hypothyroidism.

The legal concept of autonomy serves as the basis for numerous decisions protecting a person's bodily integrity. In particular, cases have held that competent adults have the right to choose whether or not to undergo medical interventions.2 Before people make such a choice, they have a right to be informed of facts that might be material to their decision,3 such as the nature of their condition and its prognosis,4 the potential risks and benefits of a proposed test or treatment,5 and the alternatives to the proposed intervention.6 In the genetics context, health care providers have been held liable for not providing the information that a genetic test is available. 7

People also have a right to be informed about and to control the subsequent use of tissue that has been removed from their bodies. 8 There is some leeway under the federal regulations governing research involving human subjects for researchers to undertake subsequent research on blood samples provided for genetic tests (as in the newborn screening context) as long as the samples are anonymous and as long as the subsequent use was not anticipated at the time the sample was collected.9 If the additional test was anticipated at the time the sample was collected, informed consent for that use should be obtained prior to the collection of the original sample.

Such an approach is thought appropriate to avert conflicts of interest, such as a physician/researcher suggesting that a patient undergo a particular test when the researcher actually wanted the tissue for the researcher's own additional use in a research or commercial project. In such a situation, the patient's autonomy is compromised even if the sample is used anonymously in the subsequent use. A report from the Office of Technology Assessment similarly stressed the importance of knowledge and consent:

The consent of the patient is required to remove blood or tissue from his or her body, and also to perform tests, but it is important that the patient be informed of all the tests which are done and that a concern for the privacy of the patient extends to the control of tissues removed from his or her body. 10

Various justifications have been offered for rules of privacy. First, some philosophers argue that privacy rights are merely shorthand expressions for a cluster of personal and property rights, each of which can be explicated without any reference to the concept of privacy. In making this argument, Judith Jarvis Thomson holds that privacy rights simply reflect personal and property rights, such as the rights not to be looked at, not to be overheard, and not to be caused distress. 12

A second justification holds that rights to privacy are important instruments or means to other goods, including intimate relations such as trust and friendship. Being able to control access to themselves enables people to have various kinds of relationships with different people, rather than being equally accessible to all others.

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