Autozygosity
Having two homologous genes at a given locus that are identical by descent; both genes are derived from the same ancestor.

Auxotroph
A mutant organism or cell that requires growth supplements that could normally be synthesized by wild-type strains. 2. A mutant microorganism that can be grown only upon minimal medium that has been supplemented with growth factors not required by wildtype strains.

Avian
Of, relating to, or characteristic of birds (members of the class Aves).

Avirulent
Unable to overcome the host's defenses; therefore, unable to sustain an infection.

Avuncular relationship
The genetic relationship between nieces and nephews and their aunts and uncles.