Agriculture Reference
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difficulty keeping them separate. Genomic analyses often support the view that such
distinctions that split close relatives are artificial contrivances. To illustrate, consider
two clearly distinct species, corn and wheat. They cannot successfully cross pollinate
to produce hybrid progeny so some people fabricate an artifice—“species barrier”—to
explain why corn genes don't mix with wheat genes. But molecular analyses show that
the genetic makeup of the two species is actually very close. And not only is there a
high degree of similarity between individual genes (aka “homology,” see discussion
below) but also the arrangement of the genes along chromosomes is similar. This
phenomenon, called “synteny,” is true for several cereal species: he chromosomes
of rice, millet, sugar cane, wheat, sorghum, and corn can be lined up in parallel, and
the specific genes will (with some exceptions) follow the same order in all. Skeptics
will, of course, argue that this is no big deal; after all, the species are all related grassy
cereals, so seeing an alignment of genes along chromosomes should come as no sur-
prise. But what about genetic synteny shared between humans and fish? Yes, genetic
similarity is sufficient to arrange chromosomes of humans and fugu fish such that
genes will appear in the same order (for details, see
http://www.ncbi.nlm.nih.gov/
Perhaps more convincing, let's consider chromosome architecture, comparing
human chromosome 21 with a fellow mammal, the mouse. Observation of the respec-
tive chromosomes shows hundreds of shared genes between man and mouse, and the
ordered sequence of the genes is also preserved along the chromosome. For example,
segments of three mouse chromosomes could be snapped together to reconstruct the
long arm of human chromosome 21 without significant loss of genetic information
or even the order of gene arrangement (
http://www.nature.com/scitable/content/
regions-of-synteny-between-human-chromosome-21-5849
). Clearly, the chromo-
some blueprint/plans for mice and men were laid down long before Steinbeck or even
Burns, but that reality still may leave us nothing but grief and pain if we fail to recog-
nize and exploit—for the sake of human and planetary sustainability—such natural
phenomena. The synteny is not as complete as with the cereals, but these examples of
genetic similarity and chromosomal structure across species should suffice to make
the point that DNA, genes, and chromosomes are not unique or proprietary to the
species that contain them.
Sloppy language by scientists certainly contributes to the “species barrier” popular
misconception, as scientists often speak of “fish genes” or “tomato genes” or “human
genes” as if each species owned a set of unique genes. In fact, most genes are com-
mon across many species, a phenomenon called genetic homology. They may dif-
fer slightly in their DNA base sequence; consequently, the protein may have slightly
different amino acid sequence, and so the resulting protein may show slight differ-
ences in performance. For example, all mammals (including humans) carry an insulin
gene, and they do so for the same reason—to regulate blood sugar content. The DNA
sequence of the human insulin gene—and the consequent amino acid sequence of
the insulin protein—differs from the bovine or porcine insulin genes only slightly,
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