Download Natural Selection acts on phenotypic variations in populations.

Enduring Understanding 1A
Change in genetic makeup of a
population over time is evolution
ESSENTIAL KNOWLEDGE 1.A.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.