4. A scientist was given permission by the CSIR to experiment on human embryos.
As he was experimenting various way to improve the features of human beings
he replaced the genes responsible for the production of squamous epithelium by
the genes producing stratified squamous epithelium. Predict what would be the
outcomes of the research. Would the zygote be developed into a normal
embryo? Why or why not?
Answers
Answer:
AThe Basic Science of Genome Editing
Publication Details
This appendix provides technical and historical context for a number of issues related to the basic science of gene therapy and gene editing. Although an effort has been made to maximize the accessibility of this material, a simpler summary of this material can be found in Chapters 3 and 4. This appendix includes detailed material on the following topics:
breakage and repair of DNA
precursors of the clustered regularly interspersed short palindromic repeats (CRISPR) system/CRISPR-associated endonuclease (Cas9) gene editing—meganucleases, zinc fingers, and transcription activator-like effector nucleases (TALENs)
development of CRISPR/Cas9
the accuracy of gene editing
enhancing the specificity of CRISPR/Cas9
quality control and quality assurance for gene editing
use of dead Cas9 (dCas9) to regulate transcription or to make epigenetic modifications
gene targeting in transgenic animals
gene editing in embryos
alternative routes to heritable germline editing
editing the mitochondrial genome
GENE THERAPY AND GENOME EDITING
The potential for gene therapy to address human disease has been evident for some years, and much progress has been made in its applications (Cox et al., 2015; Naldini, 2015). Gene therapy refers to the replacement of faulty genes, or the addition of new genes as a means to cure disease or improve the ability to fight disease. Genome editing is one aspect of gene therapy. Established approaches to gene therapy have been based on the results of extensive prior laboratory research on individual cells and on nonhuman organisms, establishing the means to add, delete, or modify genes in living organisms. Key advances include the development of techniques for generating molecular tools for cutting the DNA of genomes in specific places to allow targeted alterations in the DNA sequence. Over recent years, several such methods have been introduced and used effectively in clinical applications.
Within the past 5 years, a completely novel system has been developed based on fundamental research on bacterial systems of immunity to viral infections. The first such system to be developed for use in genome editing of human cells, known as CRISPR/Cas9, is based on RNA-guided targeting and is much simpler, faster, and cheaper than earlier methods. The ease of design, together with the remarkable specificity and efficiency of the CRISPR/Cas9 system has revolutionized the field of genome editing and reignited interest in the potential for editing of the human genome. The development of the CRISPR/Cas9 system as a programmable genome-editing tool was built on a firm foundation of earlier research.
BREAKAGE AND REPAIR OF GENOMIC DNA
Genomes and their constituent genes are made of double-stranded DNA; this DNA can be broken accidentally (e.g., by radiation) or purposefully, using proteins called endonucleases (often called nucleases) that can generate double-strand breaks (DSBs) in DNA.
Cells have mechanisms to repair DSBs in DNA, and these mechanisms can be used to generate alterations in the DNA sequence. Groundbreaking work in bacteria, yeast, and mammalian systems shows that DSBs dramatically stimulate the rate of DNA repair by nonhomologous end joining (NHEJ), in which the broken ends are reattached (see Figure A-1). Such NHEJ repair often results in the deletion or insertion of DNA sequences of varying length, which can disrupt gene function (Rouet et al., 1994).
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