Transcript learning goal 2 natural selection acts on phenotypic variations in

Unit I
Evolution
LEARNING GOAL 2
NATURAL SELECTION ACTS ON PHENOTYPIC
VARIATIONS IN POPULATIONS
Environments change and act as selective
mechanisms on populations.
 Flowering time in relation to global climate change.
 Many plants are flowering earlier now than at any time in
the last 250 years.
 A change in timing of plant flowering can disrupt the
creatures that pollinate them. Similarly, changes in timing
of plant or insect behavior can affect the birds that use
them as food supplies.
The Peppered Moth
Moth color changed after pollution from factories
changed the color of tree trunks.
 Phenotypic variations are not directed by the
environment, but occur through random changes in
the DNA and through new gene combinations
 Some phenotypic variations significantly increase or
decrease fitness of the organism and the and the
population.
Sickle cell anemia
 A mutation in the gene for the protein hemoglobin causes
misshapen blood cells and decreased ability to carry
oxygen.
 People that have sickle cell anemia, and those that carry the
mutation are immune to the malarial parasite.
DDT Resistance in Insects
Insect populations can develop resistance to
pesticides like DDT.
Some may have the genes that give them immunity
and then pass those genes on to their offspring so
that future generations are no longer impacted by
the pesticide.
Humans impact variation in other species.
 Artificial selection
Humans select traits in plants and animals by
breeding individuals with features they feel are
desirable.
Loss of genetic diversity in crop plants.
 Since the 1900s, some 75 percent of plant genetic
diversity has been lost as farmers worldwide have
left their multiple local varieties and landraces for
genetically uniform, high-yielding varieties.
 Less genetic diversity leads to more vulnerability to
pests and disease.
Overuse of antibiotics
More resistant strains of bacteria are evolving in
response to widespread use of antibiotics.
Enduring Understanding 1A
Change in genetic makeup of a population over time
is evolution
Essential Knowledge 1.A.3
Evolutionary change is also driven by random
processes.
Genetic drift is a nonselective process occurring in
small populations.
Can result in population bottlenecks when a stressful
factor such as disease, starvation, or drought kills a
great many individuals and eliminates some alleles
from a population. This greatly reduces genetic
variation.
Founder Effect
Occurs when a few individuals colonize a distant
locality and start a new population. They carry only a
small sample of the parent population’s genetic
variation.
Reduction of genetic variation within a given
population can increase the differences between
populations of the same species.
Essential knowledge 1.A.4
Biological evolution is supported by scientific evidence
from many disciplines, including mathematics.
Scientific evidence of biological evolution uses
information from geographical, geological, physical,
chemical and mathematical applications.
Molecular, morphological and genetic information of
existing and extinct organisms add to our
understanding of evolution.
Fossils can be dated by a variety of methods that
provide evidence for evolution. These include the age
of the rocks where a fossil is found, the rate of decay of
isotopes including carbon-14, the relationships within
phylogenetic trees, and the mathematical calculations
that take into account information from chemical
properties and/or geographical data.
Morphological homologies represent features shred by
common ancestry.
 Vestigial structures are remnants of functional
structures, which can be compared to fossils and
provide evidence for evolution.
Biochemical and genetic similarities, in particular
DNA nucleotide and protein sequences, provide
evidence for evolution and ancestry.
Mathematical models and simulations can be used to
illustrate and support evolutionary concepts.