1. They occupy the same gene locus on the chromosome.
2. In diploid organisms, as there are only two homologus chromosomes, there will be only two allelic states of the multiple series.
3. In haploid gametes multiple allelic series is represented by a single allelic state
4. No crossing over in known to occur between multiple alleles as they occupy the same level of the homologus chromosomes. In a cross between two alleles, the F2 generation reveals the combination of alleles.