A Look at the Promise of Gene Editing

Doc Gumshoe explains CRISPR, CAR-T and more...

By Michael Jorrin, "Doc Gumshoe", December 5, 2019

 “CRISPR” is the word in the headline that signals that the piece is going to be about gene editing.   Doc Gumshoe did not want to put that word – actually, it’s not really a word, but an acronym – in the title of this piece because gene editing is a whole lot more than CRISPR, even though the discovery of CRISPR has hugely facilitated gene editing.   I will attempt an accurate definition of CRISPR and the role of those entities a bit further on in this piece, but for now let’s look at the bigger picture.

 Gene manipulation in some form has been around for a long, long time – centuries, at least, dating from those times when nobody had the foggiest notion of what a gene was, or how it was that some but not all of the characteristics of the parent were passed on to the offspring.   The term “parent” as used here does not refer to a human Daddy or Mommy but to whichever being, animal or vegetable, that gave rise to offspring.   When hunter-gatherers selected the largest fruit from trees, brought these prizes back to their huts for dinner, and threw the pits on the dung heap, they were unknowingly practicing genetic manipulation.   From those seeds the next generation of fruit trees would grow, producing bigger fruit than their cousins in the woods.   Tulip fanatics in Holland in the 17th century were doing genetic manipulation, as were breeders of prized hogs, as well as the agronomists who gave us such mixed-breed fruits as the pluot (a cross between a plum and an apricot) and perhaps the grapefruit (a cross between a sweet orange and a pomelo, which looks like a grapefruit but is quite a bit larger, and more sour).   The grapefruit may have emerged accidentally, or it might have been a deliberate creation.   

In any case, what the creators of those hybrids (and many, many more) were doing was taking genetic material from different “parents” and putting them together such that the offspring are genetically modified – essentially different from their parents.   But they had no idea that all characteristic features of the animals and plants they were working with were encoded in genes, nor yet even of the existence of genes.   

The concept of genes and genetics came into being in the early years of the 20th century, although as yet nobody knew what a gene actually was.   Chromosomes had been identified as related to inherited characteristics, and had even been observed under the microscope at that time, but what the chromosomes actually were was still unknown.   As the capacities of microscopes progressed, it became possible to get a closer look at chromosomes, which led to the discovery in 1953 by Francis Crick and James Watson of the configuration of the DNA molecule in the chromosome, i.e., the famous double helix.   DNA in turn was found to be composed of a linking of four amino acids, termed “bases” (adenine, cytosine, guanine and thymine plus a phosphate group and a pentose sugar).   The human genome consists of about 6.2 billion bases, paired and linked together in a very long twisting chain, which itself is wound around itself so as to take up minimum space.   The genetic information is carried by these 3.1 billion base pairs, and the possibility of effecting changes to that genetic information, such as eliminating the genes that carried the information that would cause diseases or disabilities was immediately the subject of research.   

The information carried in the genome might be compared with the information embodied in computer code.   As by now everyone knows, computer code as read by the computer consists of strings of ones and zeros, which signify yesses and nos, impulse transmitted or impulse blocked.   The human entering the code does not have to translate the numbers in our decimal system into the binary system of ones and zeros – the computer takes care of that.   There doesn’t seem to be any limit to the amount of information that computer code can convey, but those strings of ones and zeros can get pretty long.

Genetic information is conveyed by that string of amino acids.   As in computer code, the information is essentially digital, except that instead of two digits to work with, the genome can use four digits, for the four amino acids – A, C, G, and T.   Thus, it can carry a good deal more information than computer code, in a limited sp