Download 1.A.2. Natural Selection Acts On Phenotype

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1.A.2. Natural Selection Acts On
Natural selection acts on phenotypic
variations in populations.
Environments change and act as
selective mechanism on populations.
The environment does not directly cause
changes in DNA, but acts upon phenotypes
that occur through random changes in DNA
Flowering time in relation to
global climate change
Crop production is sensitive to climate
change; temperature has a large impact on
the rate of plant development.
Warmer temperatures will mean reduced
crop yields.
Peppered moth
The light phenotype was favored before
the Industrial Revolution. The color
blended with the tree bark.
After the Industrial Revolution, mostly dark
colored moths were seen. They had an
advantage on dark tree bark.
Changes in genetic information may be silent
(with no observable phenotypic effects) or
result in a new phenotype.
Some phenotypic variations significantly
increase or decrease fitness of the
organism and the population.
Sickle cell anemia and
Heterozygote Advantage
DDT resistance in insects
Humans impact variation in other species.
Artificial selection
Loss of genetic diversity
within a crop species
Overuse of antibiotics leading to
increase in antibiotic resistant bacteria.
Biggest problem: overuse and improper use of
antibiotics, especially in livestock.
Directional Selection is most common
when an environment changes. One
phenotype favored over another.
the peppered moth
Stabilizing selection maintains the status
quo by favoring the mean phenotype.
human birth weight
Distruptive selection occurs when the
extreme phenotypes are favored. May
lead to speciation.
Wood Frog and Leopard Frog
Wood Frog
Breeds in early April
Leopard Frog
Breeds in mid-April
geographic variation – difference in
variation between population subgroups in
different areas
A cline is a graded change in a trait along a
geographic axis.