1.C.1: Speciation and extinction
First, let’s talk about what we know as speciation and
extinction. I’m sure we all know what extinctions, because honestly, what idiot
HASN’T heard about the extinction of the dinosaurs billions of years ago? Okay
that was mean and I’m certain that there are other homo sapiens that haven’t had the education and luck to be as
informed as you and I, but that’s beside the point! The point is, extinction
means the eradication of a species. Which means once the last organism of that
species dies, then that species is gone for good. Inexistent.
Speciation is exactly the opposite- speciation is the
phenomenon that occurs when species evolve from old species (who eventually die
off). Something called Adaptive radiation helps this along. Adaptive radiation
occurs when other species or populations disappear from an ecosystem and
surviving species evolve and replace those that once lived there. For example,
when the dinosaurs went extinct, mammals – who were rodent-like creatures at
that time – were able to evolve many times over and eventually replace them.
What does it mean to evolve? Evolving, better known as
evolution, is the process of organisms changing into new organisms (species) by
random mutations in their DNA. Every organism that ever existed has existed
because of evolution from one ancestor, billions of years ago. And all
organisms that have yet to exist will exist because of evolution. Isn’t that
interesting?
Speciation is also
the origination of biodiversity
1.C.2: Reproductive Isolation
Reproductive isolation is the phenomenon that prevents
organisms of separate species species from producing fertile offspring. Either
they produce sterile hybrids, or will not, due to species specific mating
rituals, reproduce.
There is also mechanical isolation in which the genitals
will not match up between the organisms to fertilize a gamete.
Pre-zygotic barriers prevent the fertilization of an egg,
and post-zygotic barriers ensure the organism can not reproduce or dies before
it reaches sexual maturity.
1.C.3: Populations Evolve
Now let’s talk about how populations evolve.
When an organism develops a mutation in its DNA, there are
several things that can happen. One is that it could have absolutely no effect,
having changed a nucleotide in a codon to one that codes for the same nucleic
acid. An example would be changing a CGU to a CGA, both of which codes for
Arginine and therefore will not affect the organism physically. If this
happened to turn CGU, for example, into GGU, then it would code for Cysteine
instead of Arginine. This could change a characteristic of the organism for
better or worse. An insertion (adding in a polypeptide that wasn’t there
before)or a deletion (the accidental removing of a polypeptide during the
copying of the RNA or DNA) of a nucleotide in the DNA could potentially destroy
an organism or create a new species, as it would change all DNA after the
insertion or deletion.
This image is a codon chart^ All DNA and RNA are made to
code for these amino acids.
But anyways, when organisms and the population they live in
evolve they survive if they have favorable (fit) traits that give them the
survival advantage for their environment. They then reproduce with others in
the population and form a separate species.
For example, if a population of aphids were sprayed with a pesticide and
a dozen had a genetic advantage (an evolved trait) that allowed them to
survive, they would reproduce and therefore be fit. This is an example of
adaptive evolution.
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