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An organism is much more than its genes, of course, but to understand an organism, you must first understand its genes.
Understand genes first then organism
genes encode chemical messages to build proteins that ultimately enable form and function.
Biologists would later term these variants alleles, from the Greek word allos—loosely referring to two different subtypes of the same general kind.
Mendel termed these overriding traits dominant, while the traits that had disappeared were termed recessive.
Dominant and recessive
Alexandra—still an unsuspecting carrier of the gene
Hemophilia inheritance
They are the workhorses of the biochemical world.
Proteins
If chromatin, as Morgan had suggested, was a string of beads, then proteins had to be the active component—the beads—while DNA was likely the string.
Protein and DNA analogy
THE WORD CODE, I wrote before, comes from caudex—the pith of the tree that was used to scratch out early manuscripts.
Origin of word code.
just as intimately as scratches are etched into pith.
Every mutant, they noted, was missing a single metabolic function, corresponding to the activity of a single protein enzyme. And genetic crosses revealed that every mutant was defective in only one gene.
a gene “acts” by encoding information to build a protein, and the protein actualizes the form or function of the organism.
When a “translation request” was generated by a cell, a photocopy of the original was summoned from the vault of the nucleus. This
Library analogy
The genome was an active blueprint—capable of deploying selected parts of its code at different times and in different circumstances.
Switching on
Genes make proteins that regulate genes. Genes make proteins that replicate genes. The
Make proteins that regulate and replicate genes.
The building of organs and structures, Lewis concluded, is encoded by master-regulatory “effector” genes that work like autonomous units or subroutines.
Effector genes
Viruses have a simple structure: they are often no more than a set of genes wrapped inside a coat—a “piece of bad news wrapped in a protein coat,” as Peter Medawar, the immunologist, had described them.
Simplicity of viruses
We had graduated, in short, from thinking about genes, to thinking in genes.
Technology now manipulates genes.
Proteins, recall, are the hubs of the biological world. They are the enablers and the disablers, the machinators, the regulators, the gatekeepers, the operators, of cellular reactions.
But to make a protein, one needs its gene—and here recombinant DNA technology provided the crucial missing stepping-stone.
The cloning of human genes allowed scientists to manufacture proteins—
The relationship between gene and protein
His genes created a propensity for an outcome, rather than the outcome itself.
In Marfan syndrome, for instance, a mutation in a fiberlike structural protein affects all connective tissues—tendons, cartilage, bones, and ligaments. Marfan patients have recognizably abnormal joints and spines.
when the Huntington’s gene had been mapped to chromosome four,
The consequence of inheriting two mutant copies of the CF gene can be fatal.
Huntingdon Disease
How might the mutant genes be restored to their off or on states, while allowing normal growth to proceed unperturbed?
Cancer genes
Cancer cells arise via mutation, survival, natural selection, and growth.
In an interview in the Baltimore Sun, a neurosurgeon wondered if the “crime-prone” (such as Huberty) could be identified, quarantined, and treated before they had committed crimes—i.e., via genetic profiling of precriminals.
Each cycle of copying amplified the DNA, resulting in an exponential increase in the yield of a gene. The technique was eventually called the polymerase chain reaction, or PCR, and would become crucial for the Human Genome Project.
The lesson is that the complexity apparent [in flies] is not achieved by the sheer number of genes,”
The numberof genes is not necessarily related to complexity
It has 3,088,286,401 letters of DNA (give or take a few; a more recent estimate is about 3.2 billion letters).
Features of genes
At some point in hominid evolution, two medium-size chromosomes in some ancestral ape fused to form one.
Ape chromosomes 48
An enormous proportion—a bewildering 98 percent—is not dedicated to genes per se, but to enormous stretches of DNA that are interspersed between genes (intergenic DNA) or within genes (introns).
Most DNA is not genes
The genetic code is simple: DNA is used to build RNA, and RNA is used to be build a protein.
DNA And RNA
The hominid was called a Neanderthal, after the site of its original location.
Neander valley
“Such a pattern fits the theory that the first modern humans settled the world in stepping-stone fashion after leaving Africa less than 100,000 years ago. As each small group of people broke away to found a new region, it took only a sample of the parent population’s genetic diversity.”
Humans left Africa 100,000 years ago
But if you sequence the epigenomes of a pair of twins over the course of several decades, you find substantial differences:
The epigenomes sequence differently to the genome
Chance events—injuries, infections, infatuations; the haunting trill of that particular nocturne; the smell of that particular madeleine in Paris—impinge on one twin and not the other. “on” and “off” in response to these events, and epigenetic marks are gradually layered above genes.
How slight changes at epigenetic level change the twins.
We can now try to understand the Dutch Hongerwinter,
Dutch starvation 1945
Circular influence of genes and environment
embryonic stem cells,
Stem cells
Paul Gelsinger decided to withdraw life support.
Jesse Gelsi ger dies.
The short variant, called 5HTTLPR/short, is carried by about 40 percent of the population and seems to produce significantly lower levels of the protein.
Gene implicated in anxiety.
it seems, the short variant encodes a hyperactive “stress sensor” for psychic susceptibility, but also a sensor most likely to respond to an intervention that targets the susceptibility.
More sensitive to stress and intervention.
