Natural Selection: 1.A.1. – 1.A.4
Kelly
Nienburg
September
25, 2014
Period
04 - AP Bio
This is
my version of a sort of study guide to help teach or just to refresh the memory
of others. It’s on Part 1.A of evolution- Natural Selection!
1.A.1
Natural Selection
Natural
selection is one of several mechanisms that lead to what we call Evolution. The
thought is that organisms that are fit enough to have survived, either through
adaptations or random mutations, can reproduce with other surviving organisms
randomly via Natural Selection. Favorable physical traits, or phenotypes, allowed
for these fit organisms to survive, reproduce and evolve over time.
Charles Darwin was the first to actually
find evidence to support the theory of evolution. He backed up this theory of
his with fossils that resembled modern species and drew conclusions that
although those prehistoric organisms may be extinct, their genetics still live
on in their modern descendants.
Something else Darwin studied to back up his theory was
Speciation. Speciation is the term used to describe how organisms of a family
vary. This, he presumed, was a product of population dispersal (note: edit this
to the correct term later on). He observed and recorded the physical features
of organisms in certain regions, noting that many only had a few key
differences- an example being the Galapagos finches, of which have mainly
different beak shapes, which were most likely developed according to the food
available to birds on each specific island.
1.A.2 Acts
on Phenotypes
In case
you didn’t know, phenotypes are what the physical features are called.
Genotypes are all the genes of an organism- dominant, codominant and recessive.
Phenotypes
and genotypes can change when random mutation in an organism’s DNA. They can be
affected by changes in the environment. For example- a citrus tree blooms in
response to the climate so that it can produce fruit at the optimum time to
that the seeds can germinate into new trees.
In
addition to randomly occurring, phenotypes are there to either help or hinder
the organism. For example, the peppered moth has two phenotypes for color- the
dominant dark, and recessive white. Before the Industrial Revolution of
England, 98% of peppered moths were light, and 2% were dark. During the
industrial revolution the numbers of dark peppered moths increased
exponentially due to the amount of soot covering the trees in the moths’
environment. And as such, the white ones decreased, as they were now unable to
blend in with their environment. After the Industrial Revolution ended, the
trees mostly returned to their normal, light color and the moths’ populations
returned to about what they were before the revolution.
Another
video, except this is on the Acts on Phenotypes.
1.A.3
Genetic Drift
Genetic
Drift is a change in the allele frequency by chance, not natural selection. It
usually occurs when small populations of the same species separate and
eventually evolve into new species.
Interestingly
enough, there is a mathematical equation that can calculate the allele
frequency of a population’s descendants, without evolution, through genetic
drift. This formula is known as the Hardy-Weinburg Equation of Genetic
Equilibrium.
Other factors that can cause genetic drift is when a population undergoes something called the Bottleneck Effect, which is when the population is severely reduced, leaving only a few individuals that closely inbreed to bring numbers back up to what the population to what it once was. The greatest downside to this is loss of genetic diversity, which will weaken a population. If, say, a population of closely related organisms were to be affected by a disease, it is likely very few, if any, would be diverse genetically enough to survive it. That population could easily go extinct.
Other factors that can cause genetic drift is when a population undergoes something called the Bottleneck Effect, which is when the population is severely reduced, leaving only a few individuals that closely inbreed to bring numbers back up to what the population to what it once was. The greatest downside to this is loss of genetic diversity, which will weaken a population. If, say, a population of closely related organisms were to be affected by a disease, it is likely very few, if any, would be diverse genetically enough to survive it. That population could easily go extinct.
This is the video I learned from. Hope it helps. J
1.A.4
Evidence of Evolution
There
are many factors that show the evidence of evolution- from geographical and
geological (like fossils and earth layers) to physical anatomy and chemical
properties of organisms. Even mathematic applications can be applied to further
prove evolution.
Looking
at many of today’s species, it can be physically seen that many share similar
characteristics. For example, all birds and most reptiles produce amniotic eggs
and have skeletons similar to prehistoric creatures. Vestigial structures, which are bones and the
like that are no longer used in some species, and homologous structures, which
are shared by many related species, are also evidence of evolution.
Here’s another of Paul Anderson’s educational videos. This one explains Evidence for Evolution.
Citations:
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