Genes, Brains, and Human Potential The Science and Ideology of Intelligence

126 REAL GENES, REAL INTELLIGENCE

Th e sequence of DNA comprising a gene is copied into a correspond-
ing sequence of nucleotides in mRNA. Th is is the immediate transcrip-
tional product— the transcript—of the gene. It used to be thought that the
mRNA template rigidly determines in what order amino acids are strung
together to make up one— and only one— protein:
One gene q mRNA q one protein.
Th e sequence of nucleotides copied into mRNA actually consists of cod-
ing sections, called exons, interspersed with noncoding sections that are
silent and are called introns. But the pro cesses that translate these into pro-
teins are less predictable. Th ese pro cesses remove the introns and rearrange
the exons in a variety of combinations (called exon shuffl ing; fi gure 4.6).
One obvious result is that many diff er ent proteins can be produced
from the same gene, with potentially widely diff er ent functions: one
gene → many proteins. By 2003, it was known that at least 74  percent of
human gene products can be alternatively spliced in this way. We now
know that the percentage is much higher than that. In their 2014 paper in
Nature, James  B. Brown and colleagues reported that even in a fl y, “a
small set of mostly neural- specifi c genes has the potential to encode
thousands of transcripts each through extensive alternative promoter
usage and RNA splicing” and that “the fl y transcriptome is substantially
more complex than previously recognized.”^19

DNA

mRNA

proteins

alternatively spliced proteins

1

1

1

a

a

2

2 2

2

b

b

3

3

4

4

c5

5

d6

6 6

3

3

4c5d6

FIGURE 4.6
Simplifi ed diagram of exon shuffl ing. Exons 1–6 are interspersed with introns a– d. Th e
latter are spliced out, while the exons can be combined in many diff er ent ways: one
gene yields diff er ent proteins as dictated by wider cell pro cesses.

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