SAN DIEGO — Two world-class institutions that call San Diego home have joined forces on an investigation into the DNA of koalas. The San Diego Zoo Wildlife Alliance and DNA-sequencing giant Illumina are examining the genetic information of nearly 100 koalas spanning 30 years to get a better understanding of koala retrovirus, or KoRV. Scientists suspect through growing evidence that certain variants of koala retrovirus — all koalas carry some form of it — are associated with common diseases and health issues they have, such as leukemia, lymphoma and deadly fungal infections. KoRV is baked into …