Gametes may be morphologically identical with vegetative cells or markedly differ from them,
depending on the algal group. The main difference is obviously the DNA content that is haploid
instead of diploid. Different combinations of gamete types are possible. In the case of isogamy,
gametes are both motile and indistinguishable. When the two gametes differ in size, we have heterogamy.
This combination occurs in two types: anisogamy, where both gametes are motile, but
one is small (sperm) and the other is large (egg); oogamy, where only one gamete is motile
(sperm) and fuses with the other that is non-motile and very large (egg).
Algae exhibit three different life cycles with variation within different groups. The main difference
is the point where meiosis occurs and the type of cells it produces, and whether there is more
than one free-living stage in the life cycle.