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REVIEWS
THE ADVANTAGES AND DISADVANTAGES OF BEING POLYPLOID
Luca Comai
Abstract | Polyploids organisms that have multiple sets of chromosomes are common in certain plant and animal taxa, and can be surprisingly stable. The evidence that has emerged from genome analyses also indicates that many other eukaryotic genomes have a polyploid ancestry, suggesting that both humans and most other eukaryotes have either benefited from or endured polyploidy. Studies of polyploids soon after their formation have revealed genetic and epigenetic interactions between redundant genes. These interactions can be related to the phenotypes and evolutionary fates of polyploids. Here, I consider the advantages and challenges of polyploidy, and its evolutionary potential.
NEOPOLYPLOID
A polyploid that has been produced by artificially inducing chromosome doubling.
DIPLOIDIZATION
Gradual conversion from polyploidy to diploidy through genetic changes that differentiate duplicated loci.
SUBFUNCTIONALIZATION
Retention by duplicated genes of different components of the original common function.
NEOFUNCTIONALIZATION
Acquisition of novel function by a duplicated gene.
Polyploidy is the heritable condition of possessing more than two complete sets of chromosomes. Most polyploids have an even number of sets of chromosomes, with four being the most common (tetraploidy). Polyploids are very common among plants and common among fish and amphibians, and are usually fit and well adapted. Indeed, the study of eukaryotic genomes is providing surprising proof of the evolutionary potential of polyploids: many sequenced genomes display the signature of polyploidy ancestry18. This indicates that polyploidy can bestow long-term evolutionary flexibility, instead of freezing species in a static state that is enforced by gene redundancy, as was originally proposed9.
In fact, polyploidy can be advantageous. On the basis of the phenotypic and molecular characterization of
NEOPOLYPLOIDS, it has been inferred that after polyploids form they pass through a bottleneck of instability1013,
before becoming adapted and joining the evolutionary fray as efficient competitors of their diploid relatives. Adapted polyploids that avoid extinction enter an evolutionary trajectory of DIPLOIDIZATION, during which
genomic redundancy is reduced14,15. Duplicated genes can be lost, retained or maintained as duplicates, often undergoing SUBFUNCTIONALIZATION and NEOFUNCTIONALIZA
TION16,17. Bioinformatic and theoretical analyses indicate
that these processes are often not random and that the function and properties of the encoded protein affect the outcome1825. By providing duplicated genes, polyploidization might fuel long-term diversification and...