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dogs are easily one of the most diverse
species on earth geneticists tell us
it's likely that each of them descended
from one animal the wolf these breeds
look very different from each other but
they all share much of their DNA with
those early wolves and that's what makes
them dogs now let's move inside the cell
and see how this works DNA is found in
the nucleus of the cell
it consists of a long chain of chemicals
designated by the letters a G C and T
some sections of DNA are called genes
they contain the specific instructions
for making the proteins that form the
cells that give the dog its traits in
our last episode we saw that DNA in
brown bears had mutated to form polar
bears well how does that work a mutation
in a gene occurs when there's a change
in its sequence often this results in
breaking one of the instructions for
forming the animal in this case the
mutation was in the specific gene that
determines fur color the disabled gene
is unable to give instructions to make
colored fur so the mutant fur is white
the change in bears occurred long ago
wouldn't it be great if we could observe
mutation today in real time well we're
in luck
critical work has been done in the
laboratory of Richard Lenski who worked
with a species of bacteria called a coli
the Lenski lab has been growing
generations of E coli in flasks for 30
years in the early 1990s they saw that
the descendant bacteria began to grow
faster than their ancestors that was
great news for the happiiy coli but why
was this happening
a decade later they were able to
determine the mutation that caused it
what they found was that a certain gene
in the e.coli had been destroyed losing
that gene ended up helping the bugs grow
faster then they looked at a dozen other
helpful mutant genes in the e coli and
saw that they too had been broken
mutations had left the genes either
crippled or completely disabled when
that seems odd how can breaking a gene
help the organism
imagine you have to drive to a
destination on one tank of gas or you'll
die
given the weight of your car you'll
never reach your destination on just one
tank so you toss out the hood a seat
floor mats and a cigarette lighter
the lighter degraded car gets you to
your destination and you survive so
breaking genes can help ecoli adapt to a
lab environment and broken genes helped
a polar bear adapt to the Arctic how
about our dog friends in just the past
20 years scientists have actually
discovered many mutations responsible
for traits of breeds and again the
mutations don't construct new genes most
of them break or damage pre-existing
genes for example increased muscle mass
in some breeds derives from degradation
of a myostatin gene we also know what
mutations caused a yellow coat short
tails even the loveable friendliness of
dogs towards humans compared to less
friendly wolves so a dog can be changed
by breaking genes but it comes at a high
cost the broken genes very likely will
never return to their original working
state the dachshund with short leg genes
won't be returning to anything
resembling a Labrador and we won't see
the polar bear mutate back to its old
self eating berries
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in short helpful mutations are not a DNA
upgrade getting a newer smartphone is an
upgrade it's more helpful because it has
completely new features but mutations
don't install new features in DNA they
only make changes to existing ones a
mutation is more like disabling your GPS
and may help to save your battery but it
doesn't add a new function
we're told that random mutation is the
main driver for evolutionary change and
that evolution is responsible for lower
forms being upgraded to higher ones yet
the latest scientific results show new
species are made by breaking genes by D
pollution not evolution
is there another piece of the puzzle
that we're missing is there some unknown
some x-factor that boosts the capacity
of evolution to gradually generate
higher and higher life-forms I'll let
you think about that for a bit and I'll
see you next time when we discover the
x-factor
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