Orthologs i I

B1 B2

Species 2 Species 1

Species 2 Species 1

Gene B

Duplication of gene

Ancestral gene in ancestral species

A gene may be related to similar genes in other organisms and also to other genes of similar sequence within the same organism.

FIGURE 20.14 Novel Gene Derived from Pre-Existing Modules

(A) Modular evolution of a new gene may involve the fusion of separate gene modules, or functional units. For example, the orange module of gene 1 may provide a function that complements the purple module of gene 2. If these two domains fuse they might then form a novel but functional gene. (B) The LDL receptor has domains found in several other proteins. The first part of the LDL receptor gene has seven repeated modules or functional units also found in the C9 complement factor of the immune system. The next module allows the protein to bind the cell membrane. This module is very similar to a portion of the epidermal growth factor receptor. Finally, the LDL receptor has a module that is unique.

A. Principle of modular evolution

Gene 1

Gene 2


New gene

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