Final answer:
Polyploid species with complete sets of chromosomes from two or more different ancestral species are called allopolyploids, which can cause reproductive isolation and lead to sympatric speciation.
Step-by-step explanation:
If polyploid species have complete sets of chromosomes from two or more different ancestral species, they are known as allopolyploids. Allopolyploidy occurs when gametes from two different species combine, which can lead to reproductive isolation due to the difference in chromosome sets. This reproductive isolation means that the allopolyploid organism cannot successfully interbreed with the parent species due to chromosomal differences.
Allopolyploidy is an important mechanism in sympatric speciation, where new species evolve from a parent species while inhabiting the same geographical region. Unlike autopolyploidy, where an organism has multiple sets of chromosomes from its own species, allopolyploidy involves the combining of chromosomes from different species, creating genetic diversity that can contribute to the evolution of new species with potentially beneficial traits.