A third way that gene duplicates arise is by retrotransposition.

Here the messenger RNA from a gene is reverse-transcribed to DNA, which is then integrated into the genome.

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#Section 3: Genetics, Cellular and Molecular Biology

Steady-state phase

G-actin monomers exchange with subunits at the filament ends, but there is no net change in the total length of filaments.

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Elongation phase

short oligomer rapidly increases in length by the addition of actin monomers to both of its ends, causing filament elongation

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The lag phase can be reduced or abolished entirely by adding premade nuclei.

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Nucleation phase 

Lag period (Time taken for nucleation) Rate-limiting Step.

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Nucleation phase 

Two G-actin molecules bind relatively weakly to each other, but addition of a third actin monomer to form a trimer makes the entire group more stable, acts as a nucleus for polymerization.