By: Steve Connor   July 28, 2017

The first known attempt at creating genetically modified human embryos in the United States has been carried out by a team of researchers in Portland, Oregon, MIT Technology Review has learned.
The effort, led by Shoukhrat Mitalipov of Oregon Health and Science University, involved changing the DNA of a large number of one-cell embryos with the gene-editing technique CRISPR, according to people familiar with the scientific results.

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Clustered regularly interspaced short palindromic repeats (CRISPR, /ˈkrɪspər/)[2] are segments of prokaryotic DNA containing short, repetitive base sequences. These play a key role in a bacterial defence system,[3] and form the basis of a genome editing technology known as CRISPR/Cas9 that allows permanent modification of genes within organisms.[4] In a palindromic repeat, the sequence of nucleotides is the same in both directions. Each repetition is followed by short segments of spacer DNA from previous exposures to foreign DNA (e.g., a virus or plasmid).[5] Small clusters of cas (CRISPR-associated system) genes are located next to CRISPR sequences.
The CRISPR/Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages[6][7][8] that provides a form of acquired immunity. RNA harboring the spacer sequence helps Cas proteins recognize and cut exogenous DNA. Other RNA-guided Cas proteins cut foreign RNA.[9] CRISPRs are found in approximately 40% of sequenced bacterial genomes and 90% of sequenced archaea.

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