Naturally Occurring Gene Edits

Continuing our series on the basics of Gene Editing, the topic of this post is inspired by the recent excitement and media coverage of CRISPR Gene Editing technology. View the other posts in this series!

No two individuals have exactly the same gene sequences because multiple sequences code for the same amino acid. This is the basis for DNA tests to prove paternity or predict ancestry. Most of the gene variations do not change the proteins they code for, but some do, such as genes for eye and hair color and height (for a quick recap of genes, check out this video:

Gene edit: A modification of a specific sequence of A, C, G, T units that instruct the sequence of amino acids that comprise a specific protein. The edit may or may not alter the amino acid sequence and the protein.

Therefore, fertilization of an egg, pollination of a flower, introduce gene edits in the offspring because of variations in the gene sequences of the two cells uniting.

Human genome: All of the genetic information needed for the embryonic development and adult function of a human being.

Still other gene edits occur because of “transposable elements,” first described in corn by Barbara McClintock (1), Nobel Laureate in 1983. Such “transposable elements” are common in all life forms, approximately 45% of the human genome is transposable elements and their location in individual genomes is highly variable (more on Barbara McClintock and transposons here:

Chromosome: a long string of genes attached end to end and then folded with proteins in a specific way.

The most well-studied gene edits in humans are those that cause cancer, such as the breast cancer gene, BRCA, on chromosome 13. It codes an important enzyme in DNA repair. A mutation that results in a “frame shift,” as described above results in no BRCA protein expression. Hence, its function to repair spontaneously occurring DNA mutations is inhibited, resulting in cells containing mutated DNA that lack the controls that limit cell multiplication, leading to uncontrolled cell expansion, the definition of cancer.

Gene: A specific sequence of A, C, G, T units that instruct the sequence of amino acids that comprise a specific protein. Humans have 20- to 25 thousand genes

A more recently studied naturally occurring gene edit is the 32 gene unit deletion in CCR5 on chromosome 3. The mutation results in loss of CCR5 protein on the surface of HIV target cells, rendering them resistant to HIV attachment and infection. This mutation naturally occurs in approximately 1.5% of humans (here is a good illustration of this mutation, just ignore the quiz question at the end:

Thank you for reading, next month we’ll be discussing more on gene edits, specifically gene edits for research.

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