Final answer:
Polyploidy refers to organisms with extra chromosome sets. Autopolyploids have chromosomes from a single species, allopolyploids involve the combination of chromosomes from two different species, and segmental allopolyploids have paired chromosomes with segmental differences.
Step-by-step explanation:
Polyploidy is a chromosomal alteration where a cell or organism possesses additional sets of chromosomes. In polyploidy, reproductive isolation may occur, leading to species differentiation and diversity. Scientists have identified three types of polyploids: autopolyploids, allopolyploids, and segmental allopolyploids.
Autopolyploids are individuals with multiple chromosome sets derived from a single species. This can result from errors in cell division where all chromosomes end up in one cell rather than being equally divided.
Allopolyploids are the result of reproductive interactions between two different species, combining sets of chromosomes from both species. Many cultivated crops like wheat, cotton, and tobacco are examples of allopolyploids, suggesting that polyploidy may serve as an evolutionary adaptation rather than merely an error.
Segmental Allopolyploids are a less commonly discussed type of polyploids, which may involve a combination of true allopolyploid behavior with paired homologous chromosomes carrying a segmental difference between them.
In summary, polyploidy is a prominent factor in plant diversification, and while it is more common in plants, it is generally lethal in animals. For instance, wheat's relationship with its ancestral diploid species illustrates the significance of polyploidy in plant evolution.