intercross

verb

1. To cross back over one another

   “From this trunk, like a tower, rose an enormous tenfold ramification, the branches of which crossed and intercrossed, and forked and developed, […]”

2. To breed two strains having a common ancestry with one another

   “A species varies occasionally in two directions, but owing to their free intercrossing they (the variations) never increase.”

noun

1. The act or product of intercrossing

   “Intercrosses are particularly useful with recessive mutations maintained in a small colony.”