64 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”as a unit for the preservation and propagation of those replicators.”^85
Evolution can then be reduced to a matter of competition among genes
(or segments of DNA) for abundance.
While this elegant idea concurred with the then accepted knowl-
edge of molecular biology and gained popular acceptance for several
decades, a number of limitations gradually crept in and prompted
re-examination of the concept. First, proteins and genes (if defined as
segments of a DNA molecule) do not necessarily have a one-to-one cor-
respondence. Only 2% of human DNA codes for proteins (qualifying
as true genes); the rest serves regulatory functions. By a process called
alternative splicing, segments from distant parts of a DNA molecule
(even from different chromosomes) can be bought together to form a
“paste-up” protein, while a given segment of DNA can find its way into
different proteins with diverse functions. Thus, the information trans-
fer from DNA to protein is scrambled, and DNA sequences turn out
not to be exact templates for protein molecules. The adage “one gene,
one enzyme,” or “one gene, one protein”, once thought to be infallible,
no longer holds true. What then is DNA good for? Sure enough, it is a
handbook, an encyclopedia, a reference source, a storehouse for infor-
mation, and a blueprint suitable for copying, but it is not capable of
replication or information transfer without the help of many proteins,
let alone making a live cell.
The concept of epigenetics, which posits that inheritance is not lim-
ited to the information coded in the DNA sequence, is gaining accep-
tance. The mechanisms include methylation of DNA, modification of
histone (the protein that binds DNA in the nucleus), and multiple ver-
sions of RNA interference and regulations, along with external factors
such as culture and civilization that can pass on from generation to gen-
eration.^86 Inheritance has now expanded from the “one-dimensional”
DNA to a “multi-dimensional” biological process.^87
It may be worth mentioning that in certain species of yeasts, non-
Mendelian inheritance from one cell to the daughter cells can be car-
ried out through “prion” proteins, a type of protein that exists in two