Gametes and fertilization are at least as old as animals, with many different types of external and internal fertilization and anisogamy is almost as old.    From Wordnik.com.  [Just when you thought it was safe to go in the water again ... - The Panda's Thumb] Reference

Some green algae produce gametes that differ from vegetative cells, and in some species, the male gamete differs in size or morphology from the female gamete anisogamy.    From Wordnik.com.  [Mutation, selection and complexity - The Panda's Thumb] Reference

From isogamy where both “egg” and “sperm” are one and the same, to anisogamy where the egg hecomes the larger and the sperm the smaller one to oogamy where the sperm is now flagellated and fertilizes an egg with no flagella.    From Wordnik.com.  [Mutation, selection and complexity - The Panda's Thumb] Reference