Final answer:
A polyploid organism contains three or more sets of chromosomes, with polyploidy more common in plants and associated with larger size and robustness. It arises from errors in meiosis like the fusion of an abnormal diploid egg with a normal haploid sperm, often leading to reproductive sterility.
Step-by-step explanation:
A polyploid organism is one that contains three or more sets of chromosomes. Polyploidy is a genetic condition where a cell or organism has more than two complete sets of chromosomes. Most plants and animals are diploid, having two sets of chromosomes (2n). In contrast, polyploid organisms possess multiple sets. One way polyploidy can occur is through errors during the process of meiosis, where chromosomes do not separate properly.
While polyploidy is rare in animals, it is relatively common in plants. Polyploid plants often display characteristics such as larger size and robustness, compared to their diploid counterparts. Scientists distinguish two main types of polyploidy: autopolyploidy, involving multiple chromosome sets from the same species, and allopolyploidy, which involves chromosome sets from different species.