[ExI] Why genes don’t hold all the answers for biologists

[BillK]

Despite being central to the subject for over a century, there has
never been a universally accepted, constant definition of what genes
actually are. From the beginning, scientists have tried to link human
characteristics to genes, but had limited success in establishing
stable connections.

<https://theconversation.com/why-genes-dont-hold-all-the-answers-for-biologists-92194>

Quote:
As a consequence, the function of genes is now understood to depend on
systems of epigenetic inheritance and environmental signalling.
Whether a gene is activated (or not) to produce a protein depends on
how it is “packaged” into chromosomes, and information the organism
receives from the environment.

The most important insight associated with the discovery of the gene
in the early 20th century was that the order in which genes operate
does not reflect the order in which the human (or plant or animal)
body develops. One gene is not linked to one physical trait – many
genes control many traits. Likewise, a single trait is often
controlled by hundred of genes forming complex networks of
interaction.

With the subsequent identification of DNA as the hereditary material
in 1953, it became possible to directly access and manipulate the
genetic code. Even with this discovery, however, it turned out that
genes are not well-defined stretches of DNA that translate directly
into the structure of proteins.

Genes may consist of separate building blocks that are distributed
over the genome and have different functions. They may overlap and be
read in a variety of ways. Their products in turn, may be cut into
pieces and then spliced together again in a variety of ways. All of
these activities depend on a variety of signals – from within the
cell, from other cells, or from the environment.
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So it now turns out that gene expression is both nature *and* nurture.
Well, who'd have thought that!

BillK