LEARNING GOAL 2NATURAL SELECTION ACTS ON PHENOTYPIC

VARIATIONS IN POPULATIONS

Unit IEvolution

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 1AChange in genetic makeup of a population

over time is evolution

Essential Knowledge 1.A.3Evolutionary 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 EffectOccurs 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.4Biological 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.