Final answer:
A top-heavy lineage has many species but few ancestral lineages, while a bottom-heavy lineage has many ancestral lineages but relatively few species.
Step-by-step explanation:
In biology, a top-heavy lineage refers to a group of organisms that has experienced recent rapid diversification, resulting in a large number of species with relatively few ancestral lineages. This is typically seen in groups such as flowering plants, where there are many species but relatively few common ancestors. On the other hand, a bottom-heavy lineage refers to a group of organisms that has a deep evolutionary history with many ancestral lineages and fewer extant species. An example of a bottom-heavy lineage is sharks, which have a long evolutionary history with many ancient species but relatively few living species.