Essential knowledge 4.C.1: Variation in molecular units provides cells with a wider range of functions.

Variations within molecular classes provide cells and organisms with a wider range of functions.
• Different types of phospholipids in cell membranes 
• Different types of hemoglobin 
• MHC proteins 
• Chlorophylls

• Molecular diversity of antibodies in response to an antigen Multiple copies of alleles or genes (gene duplication) may provide new phenotypes. [See also 3.A.4, 3.C.1] 

Evidence of student learning is a demonstrated understanding of each of the following:
1. A heterozygote may be a more advantageous genotype than a homozygote under particular conditions, since with two different alleles, the organism has two forms of proteins that may provide functional resilience in response to environmental stresses.
2. Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function.
To foster student understanding of this concept, instructors can choose an illustrative example such as:
• The antifreeze gene in fish

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Essential knowledge 4.C.2: Environmental factors influence the expression of the genotype in an organism.

Environmental factors influence many traits both directly and indirectly. [See also 3.B.2, 3.C.1]
To foster student understanding of this concept, instructors can choose an illustrative example such as:

• Height and weight in humans
• Flower color based on soil pH
• Seasonal fur color in arctic animals
• Sex determination in reptiles
• Density of plant hairs as a function of herbivory
• Effect of adding lactose to a Lac + bacterial culture
• Effect of increased UV on melanin production in animals
• Presence of the opposite mating type on pheromones production in yeast and other fungi


b. An organism’s adaptation to the local environment reflects a flexible response of its genome.
To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Darker fur in cooler regions of the body in certain mammal species
• Alterations in timing of flowering due to climate changes

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Essential knowledge 4.C.3:The level of variation in a population affects population dynamics.

a.  Population ability to respond to changes in the environment is affected by genetic diversity. Species and populations with little genetic diversity are at risk for extinction. [See also 1.A.1, 1.A.2, 1.C.1]

To foster student understanding of this concept, instructors can choose an illustrative example such as:
• California condors 
• Black-footed ferrets 
• Prairie chickens 
• Potato blight causing the potato famine
• Corn rust affects on agricultural crops 
• Tasmanian devils and infectious cancer

Genetic diversity allows individuals in a population to respond differently to the same changes in environmental conditions.

To foster student understanding of this concept, instructors can choose an illustrative example such as:

• Not all animals in a population stampede.

• Not all individuals in a population in a disease outbreak are equally affected; some may not show symptoms, some may have mild symptoms, or some may be naturally immune and resistant to the disease.

Allelic variation within a population can be modeled by the Hardy- Weinberg equation(s). [See also 1.A.1]

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Essential knowledge 4.C.4:The diversity of species within an ecosystem may influence the stability of the ecosystem.

. Natural and artificial ecosystems with fewer component parts and with little diversity among the parts are often less resilient to changes in the environment. [See also 1.C.1]

b. Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem. The effects of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem, and when they are removed from the ecosystem, the ecosystem often collapses.

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