A continuum of genetic predicaments is represented in this diagram, matched with a continuum of genetic rescue techniques. Technologies on the left can readily be used in conservation of living species. Emerging methods on the right make reviving extinct species possible. When combined these technologies create pathways for genetic assistance and de-extinction.
Remnant populations of endangered species often become so small and inbred that they suffer from decreasing variability in their gene pool. Their situation can be analyzed with Comparative Genomics (becoming a common practice in conservation biology). Cloning can be used for gene pool enrichment.
The “ancient DNA” of many extinct species can be recovered from museum specimens and fossils via Ancient Genome Assembly. New techniques still being further developed (Synthetic DNA and CRISPR Genome Editing) may be able to bring the reassembled genomes back to life via a close living relative. But species that died out so long ago that no DNA remains, such as dinosaurs, are unrecoverably extinct.