There are two types of polyploidy:
Polyploids are usually infertile with members
of their parent species, because diploid x tetraploid crosses produce sterile
triploid progeny. If the triploid is viable, it is infertile, due to some
chromosomes being inherited twice, others once, leading to a lack of gene
dosage balance in the gametes.
- chromosome doubling within a species.
- hybridization, followed by chromosome doubling.
One of the reasons polyploidy is commonest
in plants is that they are often hermaphrodite, and hermaphrodites can
often self. When you are the first "hopeful monster", such as a new hybrid
allopolyploid, or often just an autopolyploid part or branch of a normal
diploid individual, your only way of avoiding the production of triploid
progeny will be to mate with yourself!