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. 2014 Jun 26:6:plu029.
doi: 10.1093/aobpla/plu029.

Genome downsizing and karyotype constancy in diploid and polyploid congeners: a model of genome size variation

Lidia Poggio  1 , María Florencia Realini  1 , María Florencia Fourastié  1 , Ana María García  1 , Graciela Esther González  2
Affiliations

Genome downsizing and karyotype constancy in diploid and polyploid congeners: a model of genome size variation

Lidia Poggio et al. AoB Plants. .

Abstract

Evolutionary chromosome change involves significant variation in DNA amount in diploids and genome downsizing in polyploids. Genome size and karyotype parameters of Hippeastrum species with different ploidy level were analysed. In Hippeastrum, polyploid species show less DNA content per basic genome than diploid species. The rate of variation is lower at higher ploidy levels. All the species have a basic number x = 11 and bimodal karyotypes. The basic karyotypes consist of four short metacentric chromosomes and seven large chromosomes (submetacentric and subtelocentric). The bimodal karyotype is preserved maintaining the relative proportions of members of the haploid chromosome set, even in the presence of genome downsizing. The constancy of the karyotype is maintained because changes in DNA amount are proportional to the length of the whole-chromosome complement and vary independently in the long and short sets of chromosomes. This karyotype constancy in taxa of Hippeastrum with different genome size and ploidy level indicates that the distribution of extra DNA within the complement is not at random and suggests the presence of mechanisms selecting for constancy, or against changes, in karyotype morphology.

Keywords: Bimodal karyotype; DNA amount variation; Hippeastrum; genome size; karyotype constancy; polyploids..

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Figures

Figure 1.
Figure 1.
Mitotic metaphases of Hippeastrum species: (A) H. rutilum (2n = 22), (B) H. puniceum (2n = 33), (C) H. rutilum (2n = 44), (D) H. blossfeldiae (2n = 44), (E) H. cybister (2n = 55) and (F) H. puniceum (2n = 66). Scale bar: 10 µm.
Figure 2.
Figure 2.
Relative chromosome and arm sizes per haploid complement (x = 11): (A) H. solandriflorum (2x), (B) H. tucumanum (2x), (C) H. parodii (2x), (D) H. correiense (2x), (E) H. rutilum (2x), (F) H. morelianum (2x), (G) H. puniceum (3x), (H) H. rutilum (4x), (I) H. blossfeldiae (4x), (J) H. cybister (5x), (K) H. rutilum (5x) and (L) H. puniceum (6x). S, short arm; L, long arm; m, metacentric; sm, submetacentric; st, subtelocentric; t, telocentric.
Figure 2.
Figure 2.
Continued.
Figure 3.
Figure 3.
Asymmetry parameters (MCA and CVCL) plotted against DNA content. The bars represent the total DNA amount (2C) and the black zone indicates the basic DNA amount (1Cx). (A) H. solandriflorum (2x), (B) H. tucumanum (2x), (C) H. parodii (2x), (D) H. correiense (2x), (E) H. rutilum (2x), (F) H. morelianum (2x), (G) H. puniceum (3x), (H) H. rutilum (4x), (I) H. blossfeldiae (4x), (J) H. cybister (5x), (K) H. rutilum (5x) and (L) H. puniceum (6x). MCA, mean centromeric asymmetry; CVCL, coefficient of variation of chromosome length.
Figure 4.
Figure 4.
Total DNA content (2C) plotted against ploidy level. Solid line, linear fit; broken line, extrapolated from diploids.
Figure 5.
Figure 5.
DNA content per basic genome (1Cx) plotted against ploidy level. Solid line, linear fit/ploidy level (x); broken line, extrapolated from diploids/ploidy level (x).
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