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Even setting aside germline editing, the ethics of somatic gene therapy raise urgent justice concerns. Casgevy costs approximately $2.2 million per treatment. The gene therapy Zolgensma costs $2.1 million. These prices reflect complex manufacturing, small patient populations, and the economics of pharmaceutical development -- but they also mean that life-saving treatments are available only to patients in wealthy countries with robust insurance systems.

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. That mouthful of a name describes a pattern found in the DNA of bacteria — short, repeating sequences separated by unique spacer sequences. These spacers are actually fragments of viral DNA that the bacterium has captured and stored as a kind of genetic memory, allowing it to recognize and fight off the same virus if it ever attacks again.

The power of CRISPR comes with significant responsibility. The 2018 case of He Jiankui, who used CRISPR to edit the genomes of human embryos, sparked global outrage and led to his imprisonment. The scientific community has broadly agreed that germline editing — changes that would be passed to future generations — should not proceed until safety and ethical frameworks are firmly established.

Somatic gene editing modifies cells in a living person's body -- blood cells, liver cells, retinal cells. The changes affect only the treated individual and are not inherited by their children. From an ethical standpoint, somatic editing is broadly comparable to any other medical intervention: it requires informed consent, demonstrated safety and efficacy, and regulatory approval.

The story of CRISPR begins in 1987, when Japanese molecular biologist Yoshizumi Ishino noticed unusual repeating sequences in E. coli DNA. For years, nobody understood what they did. In the early 2000s, Spanish microbiologist Francisco Mojica proposed that these sequences were part of an adaptive immune system — bacteria's way of remembering past viral infections.

Gene editing gives humanity the ability to rewrite the code of life. CRISPR-Cas9, base editing, and prime editing can correct disease-causing mutations, disable pathogenic genes, and potentially enhance biological traits. The first CRISPR therapy, Casgevy, is already treating patients with sickle cell disease. Dozens more therapies are in clinical trials.

Having a recipe is one thing. Actually cooking the dish is another. The process of reading a gene and building the protein it encodes involves two major steps: transcription and translation. Together, they form what biologists call the Central Dogma of molecular biology. For a detailed walkthrough, visit our article on How Gene Expression Works.

Before CRISPR, editing a single gene could take months of work and cost tens of thousands of dollars. Today, a graduate student can design and execute a gene edit in a matter of days for a few hundred dollars. This democratization of genetic engineering has opened doors that were previously accessible only to the most well-funded laboratories.

In 1958, British molecular biologist Francis Crick proposed what he called the "Central Dogma." Crick, who had co-discovered the double-helix structure of DNA with James Watson just five years earlier, wanted to describe the fundamental rule governing how genetic information moves inside cells [1].

Because you inherit two copies of most genes — one from each parent — the relationship between those copies matters. This brings us to one of the oldest concepts in genetics: dominant and recessive traits, first described by Gregor Mendel in the 1860s from his experiments with pea plants [5].

Before we get to the main flow of information from DNA to protein, there is a preliminary step that makes everything else possible: DNA replication. Every time a cell divides, it must first make a complete copy of its entire DNA so that both daughter cells get a full set of instructions.

When a mutation changes a gene in a way that prevents it from producing a functional protein — or produces a harmful one — the result can be a genetic disease. There are more than 6,000 known genetic diseases, and collectively they affect about 300 million people worldwide [7].

DNA stands for deoxyribonucleic acid. It's a long, thread-like molecule found inside nearly every cell of your body. If you stretched out all the DNA from a single human cell, it would extend about 2 meters (6 feet) — yet it's packed into a nucleus just 6 micrometers across.

Imagine you are editing a long document and you need to fix a specific typo. You would use the "find" function to locate the exact word, then use "replace" to correct it. CRISPR works in a remarkably similar way, but the document is DNA and the editing tool is molecular.

Here is a fact that surprises many people: genetically, all humans are 99.9 percent identical [4]. The entire difference between you and any other person on the planet comes down to about 0.1 percent of your DNA — roughly 3 to 4 million base pairs out of 3.2 billion.

In November 2018, Chinese biophysicist He Jiankui shocked the world by announcing that he had used CRISPR to edit the CCR5 gene in human embryos, resulting in the birth of twin girls known as Lulu and Nana. A third child was born from the same experiments in 2019.

Here's the crucial insight: every cell in your body contains the same DNA, but different cells express different genes. A liver cell and a neuron have identical genomes, but they look and function differently because they've turned on different sets of genes.

For decades, RNA was treated as a boring intermediate — just the messenger between DNA (the star) and proteins (the workhorses). That perception has changed dramatically. RNA has moved to center stage in medicine and biotechnology for several reasons.

DNA stores biological information in the sequence of its bases. Just as the English language uses 26 letters to write everything from grocery lists to novels, DNA uses 4 bases to encode the instructions for building and maintaining an organism.

Germline editing modifies eggs, sperm, or embryos. Any changes made at this stage become part of the individual's genome and will be passed to all of their descendants. This is the ethical fault line that divides the gene editing debate.

To understand genes, you need to understand the molecule they are made of: DNA (deoxyribonucleic acid). If you want a deeper dive, see our full guide to What Is DNA? The Blueprint of Life Explained. Here is the short version.

RNA stands for ribonucleic acid. If DNA is the master blueprint locked in the vault, RNA is the photocopy — a temporary, working version of the instructions that gets carried out to where the actual construction happens.

Transcription is the process of copying a specific section of DNA (a gene) into a molecule of messenger RNA (mRNA). This is where the cell selects which recipes it needs right now and makes portable copies of them.

The most visceral public fear around gene editing is the prospect of "designer babies" -- using genetic modification to select or enhance traits like intelligence, athletic ability, appearance, or personality.

The language connecting mRNA to protein is called the genetic code, and it operates on a beautifully simple principle: every three consecutive nucleotide bases in mRNA (called a codon) specify one amino acid.

Understanding the Central Dogma makes it immediately clear why even tiny changes in DNA can have devastating consequences. Consider sickle cell disease, one of the most common genetic disorders worldwide.

RNA is not just one thing. Your cells produce several different types of RNA, each with a specialized job. Understanding these types is essential for grasping modern gene editing and genetic medicine.

Translation is the step where the information encoded in mRNA is finally used to build a protein. This process takes place on ribosomes — molecular machines found in the cytoplasm of the cell.

In 1953, James Watson and Francis Crick — building on X-ray crystallography data from Rosalind Franklin — described DNA's iconic structure: the double helix. Think of it as a twisted ladder:

A gene is a specific segment of DNA that carries the instructions for building one protein (or, in some cases, a functional RNA molecule). Think of a gene as a single recipe in a cookbook.

DNA stands for deoxyribonucleic acid. It is the molecule that stores your complete genetic instructions — roughly 3.2 billion "letters" of code packed into nearly every cell of your body.

While much of the conversation about genes focuses on disease, it is worth remembering that the vast majority of your 20,000 genes are working perfectly well right now. They are:

Centers for Disease Control and Prevention. "Understanding mRNA COVID-19 Vaccines." CDC, 2023. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/mrna.html

In 1958, Francis Crick proposed what he called the Central Dogma of molecular biology — a simple but powerful idea that describes how genetic information flows inside cells:

Crick's Central Dogma has held up remarkably well, but biology loves to find workarounds. Several important exceptions have been discovered since 1958.

If genetic diseases are caused by errors in genes, the obvious question is: can we fix the error? That is exactly what gene editing sets out to do.

CRISPR has moved rapidly from the laboratory to the clinic and beyond. Here are some of the most significant areas where it is making an impact.

If you are reading this on a site about gene editing, you might be wondering: why does any of this matter for technologies like CRISPR?

Where should we draw the line? The emerging consensus, fragile and contested as it is, includes several principles:

DNA doesn't float around loosely in the cell. It's organized at multiple levels:

Before we wrap up, let's clear up a few points that often trip people up:

Gene editing technologies intervene at different points in this process:

A mutation is any change in the DNA sequence. Mutations can be:

Understanding DNA structure explains why gene editing works:

Errors in gene expression underlie many diseases:

Gene expression follows two major steps: