Final answer:
The model of DNA replication with mixtures of original and new DNA portions in the strands is called dispersive replication.
Step-by-step explanation:
The model of DNA replication that suggests newly synthesized strands of DNA have mixtures of parental and newly synthesized portions is called dispersive. In conservative replication, the entire double-stranded DNA molecule is either new or original. In semi-conservative replication, which was proven to be the method of DNA replication in the Meselson and Stahl experiment, each of the two parental DNA strands serves as a template for a new DNA strand, therefore, after replication, each double-stranded DNA contains one parental strand and one new strand.