A molecular cytogenetic analysis of chromosome behavior in Lilium ...

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Chapter 4of the sexual polyploidized progenies can be aneuploids. That is why a few aneuploids werefound with one or two chromosomes missing in backcross progenies of lily after sexualpolyploidization (Khan 2009; Khan et al. 2009a; Zhou 2007). However, anaphase bridging isnot the only factor that contributes to aneuploids, at metaphase I during meiosis, numericalunivalent were also present in most of the pollen mother cells (chapter 3), the randommovements of these univalents in the first meiotic division can also lead to the production ofaneuploids (Zhou 2007). In conclusion, meiosis with anaphase bridges mostly producedunviable gametes due to chromosome number or structure variation.Fig. 4.2. Illustration of the production of chromosome bridgesanaphase I stage during meiosis of interspecific lily hybridswith different configurations at56
U-type exchanges in Lilium hybridsChromatid breakage is probably a genetic response to genomic shock caused byinterspecific hybridization in lily. Like radiation, interspecific hybridization can cause meioticinstability, which is common in many species hybrids. Our results showed that univalents,multivalents, non-homologous bivalents, bridges as well as ring chromosomes were presentduring meiosis of these lily hybrids. Similarly, univalent, chain and ring multivalents andanaphase bridges were found in the pollen mother cells of a F1 hybrid between Vignaumbellate and V. minima (Gopinathan and Babu 1986). Non-homologous chromosomepairing has also been found in the hybrids of Lolium temulentum × L. perenne. In the hybridsof Helianthus annuus × H. tuberosus, genomic alterations were revealed to be the response togenomic shock following the interspecific cross (Natali et al. 1998). These meioticabnormalities all involved chromatid breakage. Since normal meiosis can be found in both ofthe parents of the hybrids, the meiotic irregularity is probably due to interspecifichybridization. Indeed, during allopolyploid formation, interspecific hybridization, rather thanpolyploidization, is likely the reason of extensive genetic and epigenetic changes (Wang et al.2006). Furthermore, if chromosome breakage occurs at the centromere position, fusion of twobroken chromatids from one chromosome arm will probably lead to the production ofisochromosomes (see chapter 5), which has been also presumed as a mechanism leading to Bchromosomes.We propose that U-type exchanges in lily hybrids are DSBs and the repair mediated byNHEJ. It has been revealed that crossovers are indeed DSBs followed by the repair by HR(Keeney 2001; Puchta 2005; Szostak et al. 1983). In mitotic cells, DSB repair with the sisterchromatid appears to be preferred, whereas interhomolog recombination is favoured duringmeiosis (Pradillo and Santos 2011). Sequence repeats comprise a large fraction of lily genomeand, although they can be quite divergent from each other, their enormous number anddispersal throughout the genome also makes them potential repair templates. Increase of HRmediated events—such as unequal sister-chromatid exchange and ectopic HR between nonallelicrepeated DNA fragments can result in chromosomal rearrangements (Aguilera andGómez-González 2008). As a result, altered karyotypes in yeast have been explained as due toDSBs repaired either by reciprocal unequal sister chromatid recombination or ectopicrecombination between non-homologous chromosome (Loidl and Nairz 1997). However, suchexplanation doesn’t fit the current results for two reasons. Firstly, none of reciprocal unequalrecombination and ectopic recombination can produce bridges and fragments like what hasbeen found in lily (Fig. 4.1). Like in yeast, two mechanisms normally lead to variation ofchromosome size. Even there was an inversion, the chance that two fluorescence of the57
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A molecular cytogenetic analysis of
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Table of ContentsChapter 1General I
Page 8 and 9:
Chapter 1LilyLilies belong to genus
Page 10 and 11:
Chapter 1counterparts (Finnegan 200
Page 12 and 13: Chapter 1renewed interest in detect
Page 14 and 15: Chapter 1recombination, mechanisms
Page 16 and 17: Chapter 1is only an equational segr
Page 18 and 19: Chapter 1quite divergent with vario
Page 21 and 22: Chapter 2An assessment of chromosom
Page 23 and 24: Chromosome rearrangements in Lilium
Page 37 and 38: Chapter 3Elucidation of intergenomi
Page 39 and 40: Intergenomic recombination and chro
Page 49: Intergenomic recombination and chro
Page 52 and 53: Chapter 4AbstractMeiotic abnormalit
Page 54 and 55: Chapter 4There are some criteria to
Page 56 and 57: Chapter 4FISH experiments were perf
Page 58 and 59: Chapter 4was apparently shorter, wi
Page 60 and 61: Chapter 4bridges is explained as U-
Page 64 and 65: Chapter 4fragment have the same len
Page 66 and 67: Chapter 5AbstractSupernumerary (B)
Page 68 and 69: Chapter 5their origin, the structur
Page 70 and 71: Chapter 5Fig. 5.1. Discovery of B c
Page 72 and 73: Chapter 5In order to investigate th
Page 74 and 75: Chapter 5Centric breakage and fusio
Page 76 and 77: Chapter 5It has not, however, been
Page 78 and 79: Chapter 6The results presented in t
Page 80 and 81: Chapter 6model for molecular cytoge
Page 82 and 83: Chapter 6Fig. 6.2. The meiosis proc
Page 84 and 85: Chapter 6over events during FDR mei
Page 86 and 87: Chapter 6been detected with GISH an
Page 88 and 89: Chapter 6Another feature caused by
Page 91 and 92: ReferencesAbe, H.A., Nakano, M.N.,
Page 93 and 94: ReferencesChen, Q., and Armstrong,
Page 95 and 96: ReferencesHartlerode, A.J., and Scu
Page 97 and 98: ReferencesLarson, S.R., Kishii, M.,
Page 99 and 100: ReferencesMcClintock, B. 1931. Cyto
Page 101 and 102: ReferencesRai, R., Zheng, H., He, H
Page 103 and 104: ReferencesStewart, R.N. 1947. The m
Page 105: ReferencesZhang, L., Pickering, R.,
Page 108 and 109: Summarychromosome rearrangements. T
Page 111 and 112: SamenvattingLelie (Lilium) is in de
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Samenvattingaantal 35 met daarnaast
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摘要百合系百合科百
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Acknowledgements淡看世事去
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Curriculum VitaeSonglin Xie was bor
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Education Statement of the Graduate
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