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Lisa Alexander

; however, may lead to some pollen or egg cells that contain no chromosomes and some that contain two sets of chromosomes ( Bretangolle and Thompson, 1995 ). Pollen or egg cells that contain a double set of chromosomes are termed “unreduced gametes.” The

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David M. Czarnecki II and Zhanao Deng

formation of unreduced gametes (pollen and/or eggs). When an unreduced gamete unites with another unreduced gamete (bilateral) or with a normal haploid gamete (unilateral), the union leads to sexual polyploidization. To a certain extent, polyploidization via

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Jason D. Lattier and Ryan N. Contreras

., 2013 ; Lattier, 2016 ; Parris et al., 2010 ; Shearer and Ranney, 2013 ). Polyploidy, or whole genome duplication, is a driving force in evolution and occurs naturally through somatic mutations in meristematic cells and through unreduced gametes

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Ryan C. Graebner, Hsuan Chen, Ryan N. Contreras, Kathleen G. Haynes and Vidyasagar Sathuvalli

frequency of unreduced gametes. Van Suchtelen (1976) produced a low frequency of triploids and concluded that triploid clones generally resembled their tetraploid siblings in terms of morphology and yield. Finally, De Maine (1994) found that tetraploid

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Keri D. Jones, Sandra M. Reed and Timothy A. Rinehart

produced experimentally from hybridization of tetraploid and diploid individuals, but in nature, they usually arise from the union of unreduced (2n) and haploid (n) gametes. Unreduced gametes have been documented in many plant species ( Harlan and De Wet

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Whitney D. Phillips, Thomas G. Ranney, Darren H. Touchell and Thomas A. Eaker

unreduced gametes ( Ramsey and Schemske, 1998 ; Rounsaville et al., 2011 ). Flow cytometric screening of seeds and/or seedlings can often elucidate these reproductive pathways ( Eeckhaut et al., 2005 ; Matzk et al., 2000 ). Diploid plants, with standard

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Todd J. Rounsaville, Darren H. Touchell and Thomas G. Ranney

reported to be highly infertile ( Rayburn et al., 2009 ). However, in some cases, triploids can have limited fertility resulting from formation of apomictic embryos, unreduced gametes, and the union of aneuploid gametes ( Lim et al., 2003 ; Lo et al., 2009

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David M. Czarnecki II and Zhanao Deng

( Czarnecki and Deng, 2009 ), we performed ploidy analysis of more than 1500 lantana progeny from self, open, and/or controlled pollinations and observed frequent production of unreduced female gametes (UFGs) in some lantana cultivars/breeding lines. The

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Brian M. Schwartz, Ryan N. Contreras, Karen R. Harris-Shultz, Douglas L. Heckart, Jason B. Peake and Paul L. Raymer

arose from the union of a normal gamete with an unreduced egg or pollen grain (B III or 2 n + n hybridization) stemming from nondisjunction of chromosomes during the reductional division of meiosis I, or the equational division of meiosis II. This

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Thomas Ranney* and Thomas Eaker

Information on ploidy levels is extremely valuable for use in plant breeding programs. Fertility, crossability, and heritability of traits are all influenced by ploidy levels. Knowledge of reproductive pathways, including occurrence of apomixes, pseudogamy, and formation of unreduced gametes can also be important information for developing breeding strategies. Although ploidy level can be determined by counting chromosomes, flow cytometry provides a reliable and much faster means for determination of nuclear DNA content and associated ploidy level. Measurement of ploidy levels of seeds (embryo and endosperm) can also provide useful insights into reproductive pathways. The objective of this study was to determine the approximate genome size, estimated ploidy level, and range of reproductive pathways of a diverse collection of flowering crapbapples (Malus spp.). Genome sizes were calculated as nuclear DNA content for unreduced tissue (2C). Results from the taxa included in our survey showed DNA contents ranging from 1.52 to 1.82 for diploids, 2.40 to 2.62 for triploids, and 3.36 to 3.74 pg/2C for tetraploids. Based on these ranges, we identified 43 diploid, 10 triploid, and 4 tetraploid crabapple taxa in this collection. Results from open pollinated seeds and seedlings demonstrated a variety of reproductive pathways including apomixes and unreduced gametes. This research provides information on ploidy levels and reproductive pathways of flowering crabapples and will allow for more systematic and efficient progress in the development of improved cultivars.