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. Examples include:

• 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. 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. Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function. Examples include:

• The antifreeze gene in fish

Students should be able to:

LO 4.22 construct explanations based on evidence of how variation in molecular units provides cells with a wider range of functions.