"Two genes are said to be paralogous if they are derived
from a duplication event, but orthologous if they are
derived from a speciation event."
The differences between orthologous and paralogous genes
may be made clearer by studying the illustration
- A gene called A in species w
- is duplicated producing initially two copies of
- With time the two copies diverge by evolution forming
related genes A1 and A2. These two genes are said to be
paralogous to one another.
Paralogy typically involves comparisons within a
- Two species, x and y evolve from species w, their
common ancestor. The descendants of the A1 and A2 genes
are now called A1x, A1y, and A2x, A2y to reflect which
species they now occupy. A1x is
orthologous to A1y and A2x
is orthologous to A2y. The
comparison is between two species. A1x and A2y are
paralogously related as are A2x and A1y.