A seedling is a new iris variety, raised from seed by the hybridizer. A named variety is properly called a cultivar. Crossing an iris with itself is called a self cross. Crossing a seedling with one of its parents is a backcross. Chromosomes are the microscopic structures that carry an organism's genes.
Most organisms have multiple sets of chromosomes.
Tetraploid plants are usually larger, show more variations, and have advantages in breeding.