Horizontal gene transfer is the movement of genetic information written in DNA between different organisms. Multiple segments of DNA can be transferred at once to fellow species members (this is e.g. how antibiotic resitence of bacteria s created) or other species.
In contrast to the vertical transmission of genes during organismal reproduction, genes transferred horizontally do not always become genes that pass to organismal offspring. Three typical mechanisms of horizontal gene transfer in microbes are transformation, the uptake of nucleic acids; transduction, virus-mediated gene transfer; and conjugation, plasmid-mediated gene transfer.
One-sixth of the genes in the tardigrade genome were found to have been acquired through horizontal transfer, which might possibly influence their exquisite resilience to extreme environmental conditions.