Biological Sciences
Polyploidy
Polyploidy refers to the condition in which an organism has more than two complete sets of chromosomes. This can occur naturally or be induced artificially. Polyploidy can lead to increased genetic diversity and can have significant effects on the phenotype of an organism. It is commonly observed in plants and can contribute to their adaptation and evolution.
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11 Key excerpts on "Polyploidy"
- Cheryl Natividad(Author)
- 2019(Publication Date)
- Delve Publishing(Publisher)
On the other hand, aneuploidy is having less or more than the normal chromosome number but the number of excess or missing chromosomes is less than the haploid set. Aberrant euploidy Sexually-reproducing animals have diploid chromosome number as a result of combining the haploid sets contributed by the paternal and maternal gametes during fertilization. The haploid chromosome number is normally Genetics 25 observed in gametes. In contrast, some insects like male bees, wasps, and ants have only one set of chromosomes, a condition known as monoploidy . However, monoploidy is abnormal for diploid organisms. Polyploidy is having more than two sets of chromosomes (or genomes) such as three sets (a condition known as triploidy ), four sets ( tetraploidy ), five sets ( pentaploidy ), and so on (see Figure 1.17). There are two types of Polyploidy, autoPolyploidy which results from the addition of extra sets of chromosomes that are identical to the characteristic haploid genome of the organism and alloPolyploidy which is a product of mating between two related but different species so that the hybrid offspring possesses different genomes. In animals, those that are monoploids or polyploids usually do not survive beyond the embryo stage but certain groups of fish and amphibians are polyploids (Woodhouse et al ., 2009). Polyploid plants are prevalent but may have traits that differ from their diploid counterparts such as larger cell size and a greater number of cells leading to larger flower and fruit size. Additionally, polyploid plants may show increased vigor and even outperform the diploid ones in terms of yield and tolerance to biotic and abiotic stresses. On the other hand, plant autopolyploids often have reduced fertility as they also produce gametes with abnormal chromosome number. This is exploited to produce seedless varieties of certain crops such as watermelon and commercial bananas (Sattler et al. , 2016; Klug et al ., 2006).
No longer available |Learn more- André Gallais(Author)
- 2003(Publication Date)
- Inra(Publisher)
1Some general aspects of autopolyploid genetics
1. Types and occurrence of polyploids
A genome can be defined as the basic set of chromosomes found in the gametes of a diploid species. The level of ploidy refers then to the number of genomes that constitute a cell nucleus. Since Kihara and Ono (1926) two broad categories of polyploids are commonly recognized: autopolyploids, where the genomes are homologous, and allopolyploids which combine non-homologous genomes from more than one ancestral diploid species (Fig 1.1 ). In what follows we mainly consider polyploids with an even number of each genome, which ensures a normal meiosis for both kinds of polyploids. Consequently, ploidy level of autopolyploids is denoted by 2v , with v = 1 for diploids, 2 for autotetraploids, 3 for autohexaploids, etc. The chromosome number of an autopolyploid can then be denoted by 2vx where x is the basic haploid number, while that of an allopolyploid might be denoted 2(x , y ) or 2(x , y , z ) if there are two or three different genomes.Polyploidy is widespread in plants: the estimated frequency of polyploid taxa ranging from 30 to 35% (Stebbins, 1971) and up to 70% (Averett, 1980; Goldblatt, 1980), depending upon the method of estimation. Polyploidy also occurs in fungi, insects, amphibians, reptiles, and fishes (Sexton, 1980) but more sporadically. As extreme examples of supposed autoPolyploidy in plants, Sedum suaveolens has 80 times a genome of 8 chromosomes (Uhl, 1978) and the fern Ophioglossum pycnostichum has 84 times a set of 15 chromosomes (Love et al., 1977). Several major cultivated plants are either allopolyploid like wheat and rapeseed, or autopolyploid like sugarcane, lucerne and potato (Table 1.2
eBook - PDF- Ibrokhim Y. Abdurakhmonov(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
Part 2 Cytological Technologies 4 Use of 2n Gametes in Plant Breeding A. Dewitte 1 , K. Van Laere 2 and J. Van Huylenbroeck 2 1 KATHO Catholic University College of Southwest Flanders, Department of Health Care and Biotechnology, 2 Institute for Agricultural and Fisheries Research (ILVO), Plant Sciences Unit, Belgium 1. Introduction Genome doubling (polyploidization) has played a major role in the evolution and diversification of the plant kingdom and is regarded as an important mechanism of speciation and adaptation in plants (Otto & Whitton, 2000). The term ploidy refers to the number of basic chromosome sets (represented by ‘x’) present in a somatic plant cell (2n) or gamete (n). Scaling whole sets of chromosomes up or down is a powerful and commonly applied strategy to produce altered genotypes for breeding purposes. Polyploids differ from their diploid progenitors in morphological, ecological, physiological and cytological characteristics. Their wider geographical distribution reflects the variety of their ecological tolerances (Carputo et al., 2003; Chen, 2007; Knight et al., 2005; Otto & Whitton, 2000; Soltis & Soltis, 2000; Thompson et al., 2004). Polyploids have breeding value as they can have broader and thicker leaves, larger flowers, longer internodes, fewer stems per plant, fewer inflorescences, higher vegetative yields, more compact plants, greater tolerance to environmental stress, higher (additive) resistance to several diseases, increased seed weight but fewer seeds or higher chlorphyll production. Doubling the chromosome number can rescue and stabilise interspecific hybrids that would otherwise show a high degree of sterility due to failure in meiosis. Furthermore, Polyploidy might result in the development of sterile cultivars (e.g. triploids), loss of self-incompatibility, flowering time variation, changes in growth vigour or shifts in reproductive system (e.g. to asexual reproduction).
eBook - PDFIntroducing Genetics
From Mendel to Molecules
- Alison Thomas(Author)
- 2014(Publication Date)
- Garland Science(Publisher)
For example, fetal cells are obtained by amniocentesis or chorionic villi sampling 118 CHAPTER 8 Variation in Chromosomal Number and Structure (Patau syndrome) and trisomy 18 (Edwards syndrome). Both syndromes result in severe malformations and early death. Trisomies of all other human chromosomes, except chromosome 1, are known, but the affected fetuses are spontaneously aborted. Trisomy of chromosome 1 probably produces such profound changes to the human phenotype that death occurs at a very early embryological stage and so it is not detected. Chromosome 1 is one of the largest human chromosomes with, therefore, a large number of genes to be affected by the imbalance in chromosome complement. It would appear, therefore, that normal eukaryotic development requires a pre-cise diploid complement of chromosomes. Losing or gaining chromosomes so severely disrupts the delicate balance that normal development is often impos-sible. Yet, as was illustrated by the Jimson weed, this is not necessarily the case in plants. Trisomies, in particular, can result in useful variants. Indeed, it can be even more positive for plants to have extra sets of chromosomes – to be polyploid . 8.5 Polyploidy Polyploidy describes a genome with three or more complete sets of chromosomes. It is a widespread phenomenon among plant species: one-third of all genera are believed to contain polyploid species. Polyploid plants tend to grow more vigor-ously and are larger than their diploid relatives, producing larger flowers and fruit (Figure 8.5). Not too surprisingly, therefore, many commercially grown plants are deliberately produced polyploids! A selection of polyploid plants is listed in Table 8.1. Polyploidy is, however, rare among animals and it is hard to find examples of polyploid animal species. Known polyploid invertebrates include flatworms, earthworms, and brine shrimps.
- William A. Stini(Author)
- 2011(Publication Date)
- De Gruyter Mouton(Publisher)
Polyploidy in Humans and Other Vertebrates FATHI ABDEL-HAMEED Each species has a characteristic chromosomal number and morphology. In higher plants and animals, the nuclei of the somatic tissues contain two similar sets, or a diploid number (2n) of chromosomes. One set is donated by a haploid male gamete and represents the paternal genome, while the other represents the maternal genome. A degree of variability in the karyotypes of members of a given species is common in natural popula-tions. If variability involves deviation from normal structure for certain chromosomes, it is described as a structural aberration, while changes in chromosome number are described as numerical aberrations. Under normal conditions, various somatic tissues show the same ploidy level, i.e., homogeneous for diploidy. Infrequently, however, an individual may possess more than one cell, an occurrence known as mosaicism. In tissue cultures, especially long-term cultures, a progressive alteration in chromosome constitution over time can result in heteroploid cell lines, i.e., cell lines showing great variation in chromosomal number. The chromosome number of a single somatic cell can differ from diploidy in two ways: (1) in the case of aneuploidy, the chromosome number is anything other than an exact multiple of the basic number ( Λ :) or of the haploid number (1«) of a true diploid; and (2) in the case of true Polyploidy or euploidy, the chromosome number is exactly three or more times the gametic number of a true diploid or that of a hypothetical diploid (3 n, An,. . . etc.). Various forms of aneuploidy, including mono-somy (In — 1), nullisomy (2 η — 2), trisomy (2 η + 1), double trisomy (2 η + 1 + 1), and tetrasomy (2η + 2), have been observed in several plant and animal groups. Since the discovery of the first known aneuploid condition in man, trisomy 21 (Lejeune et al. 1959), several other autosomal and sex-chromosome aneuploidy conditions have been described, and it has
eBook - PDF- Jonathan Wright(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
19 Polyploidy, Aneuploidy, and Haploidy Definitions Individual chromosomes are classified as homologous (having similar structure and genes) or nonhomologous (having different structure and genes). A normal diploid plant contains η pairs of homologous chromo-somes, each pair being nonhomologous to the other pairs. A normal diploid also contains two complete sets of η chromosomes, all chromo-somes in one set being homologous to one chromosome in the other set. A tree's chromosome complement is termed haploid, diploid, triploid, tetraploid, pentaploid, hexaploid, or octoploid according to whether it contains In, 2n, 3n, 4n, 5n, 6n, or 8n chromosomes, respectively. Trees with three or more complete sets of chromosomes are collectively termed polyploids. Sometimes in evolutionary literature a distinction is made between the x-number (x is the number in a remote ancestor) and the η-number (n is the number in a modern normal plant), but this distinction will not be made here. Trees having more or less than complete sets of chromosomes [2n — 1), (3n + 2 ) , etc.] are collectively called aneuploids (meaning not true ploids). Polyploids can be subdivided according to whether the chromosome sets are derived from the same parental species ( autopolyploids ) or different parental species (allopolyploids). The prefixes auto- (meaning self) and alio-(meaning other) may also be used to form words such as autotetraploid, allohexaploid, etc. In a typical autotetraploid there 399 400 / 19. P O L Y P L O I D Y , A N E U P L O I D Y , AND HAPLOIDY are four sets of homologous chromosomes. In a typical allotetraploid, chromosomes of one species are different enough from those of the other species that there are only two sets of homologous chromosomes. Numer-ous intermediate conditions occur. Colchicine (derived from the autumn crocus, Colchicum) and podophyllin (derived from the may apple, Podophyllum) are two chemi-cals used specifically to double chromosome numbers in plants.
eBook - PDF- David Briggs, S. Max Walters(Authors)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
Wheat, Peanut, Spartina anglica and Arabidopsis suecica. A. Key concepts in the study of polypoidy 301 B. Recent insights into Polyploidy from molecular studies Key questions about Polyploidy and its significance In the next sections a number of key questions concerning Polyploidy are examined that have long intrigued biologists. How many species are Polyploidy and given the complex reticulate patterns of variation found in polyploid groups, what are the taxonomic challenges in naming and classifying species? What mechanisms operate in nature that give rise abruptly to polyploid individuals from parental stocks? Once formed, what, if any, immediate genetic changes occur in polyploids? What ecological and reproductive ‘hurdles’ do polyploids face in becoming established in plant communities? What are the characteristics of polyploids as a group? What changes in breeding behaviour are associated with Polyploidy? Is there any evidence for introgressive hybridisation in groups containing polyploids? And, in considering where our understanding of Polyploidy is still incomplete, what is the evolutionary significance of Polyploidy? Molecular approaches have contributed to a flood of important new insights into Polyploidy that often challenge the views of the past (Soltis, Visger & Soltis, 2014). How many species are polyploid? Evidence bearing on this question comes from a number of sources: morphological investigations, chromosome counts, and genome studies. First, it is essential to consider how species are delimited in polyploid groups. Then, the historic information on chromosome numbers is examined. Finally, we consider recent findings from the studies of plant genomes that have cast new light on the frequency of Polyploidy. The delimitation of taxa within polyploid groups Polyploids are formed by the addition of like or unlike genomes.
eBook - PDFChromosome Engineering in Plants
Genetics, Breeding, Evolution
- P.K. Gupta, T. Tsuchiya(Authors)
- 1991(Publication Date)
- Elsevier Science(Publisher)
These terms were defined by Kihara and Ono (1926) in the following way (my translation): 4 We understand autoPolyploidy as the doubling of the same chromosome set; alloPolyploidy is the combination of two different chromosome sets from a hybrid followed by an increase in chromosome number. The definition of autoploidy is clear and the hybrids referred to had much reduced chromosome pairing.' It is a commonly held view that alloploids are derived from hybrids between species or genera and that alloploid chromosome pairing is a consequence of structural and genetical divergences accompanying speciation. Apparently, Kihara and Ono (1926) were of the opinion that alloploidy resulted only from chromosome doubling of interspecific or intergeneric hybrids. But enough evidence has now accumulated to show beyond a reasonable doubt that alloploid pairing behavior can be under relatively simple gene control, and mutations that affect chromosome pairing may occur within a species. Therefore, alloploid pairing behavior should be used to describe polyploids 168 R. C. Jackson that do not have autoploid pairing behavior. This requires that we be able to quantify autoploid pairing behavior and to statistically test for goodness of fit to expected numbers of different meiotic configurations. The following models and equations are directed toward this goal. 3.1. A u t o p o l y p l o i d M o d e l s a n d E q u a t i o n s Only a very simple model is presented here to show general methodology. More details are given by Jackson and Casey (1982) and Jackson and Hauber (1982).
eBook - PDF- Hong-hwa Chen, Wen-huei Chen(Authors)
- 2011(Publication Date)
- World Scientific(Publisher)
The application of these methods to develop a comprehensive poly-ploid breeding program for Phalaenopsis orchids is presented in this chapter. 2.1.1. EndoPolyploidy and its occurrence in plants EndoPolyploidy, the occurrence of different ploidy levels among cells of an organism, is commonly observed in angiosperms and other plant species (Barow and Meister, 2003; Barow, 2006). It is fre-quently observed to be organ-specific and related to plant devel-opment. Mature organs with a high degree of endoPolyploidy have been detected in Arabidopsis (Galbraith et al. , 1991) as well as other plants (Barow, 2006). EndoPolyploidy is generated by endoreduplica-tion, a process in which mitosis does not occur completely after DNA replication (Larkins et al. , 2001; Barow, 2006; Inze and De Veylder, 2006). Due to the increase in gene redundancy, endoPolyploidy can boost metabolism, improve crop yield and quality (Comai, 2005), and EndoPolyploidy in Phalaenopsis Orchids and Its Application 27 also accelerate growth and enhance physiological functions (Barow, 2006). 2.1.2. EndoPolyploidy in orchid species EndoPolyploidy has been reported in several species and hybrids of orchids, such as in Dendrobium spp. (Jones and Kuehnle, 1998), Pha-laenopsis spp., Oncidium varicosum (Lin et al. , 2001; Lee et al. , 2004), Vanda (Alvarez, 1968; Lim and Loh, 2003) and Spathoglot-tis plicata (Yang and Loh, 2004). Diverse endoPolyploidy patterns are observed in leaves, roots and flowers of different species, where endoPolyploidy is concurrent with maturation or aging. Moreover, these studies also showed that the degree of endoPolyploidy was organ specific. In a study of the distribution of endopolyploid nuclei in different tissues of Phalaenopsis equestris , including the flower, leaf and root, it was reported that endoPolyploidy was related to organ development (Lin et al. , 2001).
eBook - PDF- J. -N. Volff, M. Schmid(Authors)
- 2008(Publication Date)
- S. Karger(Publisher)
Volff J-N (ed): Plant Genomes. Genome Dyn. Basel, Karger, 2008, vol 4, pp 1–12 PaleoPolyploidy and its Impact on the Structure and Function of Modern Plant Genomes A.H. Paterson Plant Genome Mapping Laboratory, University of Georgia, Athens, Ga., USA Abstract Partial or complete genome duplication is a punctuational event in the evolutionary his-tory of a lineage, with permanent consequences for all descendants. Careful analysis of bur-geoning cDNA and genomic sequence data have underlined the importance of genome duplication in the evolution of biological diversity. Of singular importance among the conse-quences of paleoPolyploidy is the extensive loss (or degradation beyond recognition) of duplicated genes. Gene loss complicates genome comparisons by fragmenting ancestral gene orders across multiple chromosomes, and may also link genome duplication to speciation. The recent discovery in angiosperms of gene functional groups that are ‘duplication-resistant’, i.e. which are preferentially returned to singleton status following genome dupli-cations, adds a new dimension to classical views that focus on the potential advantages of genome duplication as a source of genes with new functions. The surprisingly conservative evolution of coding sequences that are preserved in duplicate, suggests still additional new dimensions in the spectrum of fates of duplicated genes. Looking forward, their many inde-pendent genome duplications, together with extensive sets of computational and experimen-tal tools and resources, suggest that the angiosperms may play a major role in clarifying the structural, functional and evolutionary consequences of paleoPolyploidy. Copyright © 2008 S. Karger AG, Basel Prevalence and Phylogenetic Distribution of PaleoPolyploidy Partial or complete genome duplication is a punctuational event in the evolu-tionary history of a lineage, with permanent consequences for all descendants – if the lineage survives.
eBook - PDF- David M. Green, Stanley K. Sessions(Authors)
- 2012(Publication Date)
- Academic Press(Publisher)
The existence of morphologically identical, diploid-polyploid cryptic species pairs (Bogart and Wasser-man, 1972) indicates autopolyploidization but also suggests recent and sudden evolutionary steps. In such cases, there has not been sufficient time for diversification, nor for the elimination of the diploid population. This kind of polyploidization is thought to be a singularly rapid process of speciation, established, as it were, in one generation and contrary to speciation by isolation, which proceeds slowly and gradually through many generations (Batistic et al., 1975). Among the Anura, several taxa of naturally occurring bisexual po-lyploids have been reported. They include the following genera: Odonto-phrynus {An), Ceratophrys (8AZ), Pleurodema {An), Eleutherodactylus (8n), and Neobatrachus {An) in the family Leptodactylidae; Bufo {An) in Bufoni-dae; Pyxicephalus {An) and Dicroglossus {An) in Ranidae; Hyla {An) and Phyllomedusa {An) in Hylidae; and Xenopus in the Pipidae (Begak et al., 1966, 1970; Bogart, 1967; Barrio and Rinaldi de Chieri, 1970a,b; Wasser- 12. Polyploidy and Cytogenetic Variation in Xenopus 283 AutoPolyploidy AlloPolyploidy AA AA ACT T Parental generation AA T AB T AQ Gametes ACf x BO AA A * * I I Duplication AAO + X * AAO i AAA AAAA i AAQCf Fi generation Gametes F 2 . generation Gametes F 3 generation Gametes AB | I Duplication ABO , x + x , Acf BCf 1 AAB Duplic AAB 9 X BCf 1 AABB 1 AB 00* + 1 ABB ation ABB 9 X AO* 1 AABB | 1 AB 00* + Figure 14. Schematic representation of auto- and allopolyploidization. The boxes indicate consecutive generations: parental, F 1# F 2 , and F 3 . The capital letters A and B show number of chromosome sets of two different species. In the case of autoPolyploidy, an original 2n genome of particular species AA has undergone duplication, which results in diploid gametes: egg AA 9 or sperm AA 6 .
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