DOCSLIB.ORG

Genetic Mapping in Polyploids Genetic Genetic Mapping in Polyploids Genetic

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Genetic Mapping in Polyploids Genetic Genetic Mapping in Polyploids Genetic GeneticGenetic mapping mapping InvitationInvitation Genetic mapping in polyploids Genetic mapping in polyploids in polyploidsin polyploids You are cordiallyYou are invitedcordially to invited to attend theattend public the defense public defense of my PhDof thesis my PhD entitled: thesis entitled: GeneticGenetic mapping mapping in polyploidsin polyploids on Fridayon 15 Fridayth June 152018th June 2018 at 11:00 in at the 11:00 Aula in ofthe Aula of WageningenWageningen University, University, Generaal GeneraalFoulkesweg Foulkesweg 1, 1, Wageningen.Wageningen. Peter M. Bourke Peter Peter M. Bourke Peter Peter BourkePeter Bourke [email protected]@wur.nl ParanymphsParanymphs Michiel KlaassenMichiel Klaassen Peter PeterM. Bourke M. Bourke [email protected]@wur.nl 2018 2018 Jordi PetitJordi Pedro Petit Pedro [email protected]@wur.nl Propositions 1. Ignoring multivalent pairing during polyploid meiosis simplifies and improves subsequent genetic analyses. (this thesis) 2. Classifying polyploids as either autopolyploid or allopolyploid is both inappropriate and imprecise. (this thesis) 3. The environmental credentials of electric cars are more grey than green. 4. ‘Gene drive’ technologies display once again that humans act more like ecosystem terrorists than ecosystem managers. 5. Heritability is a concept that promises much but delivers little. 6. Awarding patents to cultivars or crop traits is patently wrong. 7. The term “air miles” should refer to one’s lifetime allowance of fossil- fuelled air travel. 8. The Netherlands’ most effective educational tool comes on two wheels with a bell. Propositions belonging to the thesis, entitled “Genetic mapping in polyploids” Peter M. Bourke Wageningen, 15th June 2018 Genetic mapping in polyploids Peter M. Bourke Thesis committee Promotor Prof. Dr R.G.F. Visser Professor of Plant Breeding Wageningen University & Research Co-promotors Dr C.A. Maliepaard Associate professor, Plant Breeding Wageningen University & Research Dr R.E. Voorrips Senior scientist, Plant Breeding Wageningen University & Research Other members Dr J. Endelman, University of Wisconsin-Madison, USA Prof. Dr M.E. Schranz, Wageningen University & Research Dr J.W. van Ooijen, Kyazma B.V., Wageningen Prof. Dr B.J. Zwaan, Wageningen University & Research This research was conducted under the auspices of the Graduate School of Experimental Plant Sciences (EPS) Genetic mapping in polyploids Peter M. Bourke Thesis submitted in fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus, Prof. Dr A.P.J. Mol, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Friday 15 June 2018 at 11 a.m. in the Aula. Peter M. Bourke Genetic mapping in polyploids, 306 pages. PhD thesis, Wageningen University, Wageningen, the Netherlands (2018) With references, with summary in English ISBN 978-94-6343-846-9 DOI 10.18174/444415 Table of contents Chapter 1 General Introduction 7 Chapter 2 Tools for genetic studies in experimental populations of polyploids 27 Chapter 3 The double reduction landscape in tetraploid potato as revealed by a high-density linkage map 53 Chapter 4 Integrating haplotype-specific linkage maps in tetraploid species using SNP markers 77 Chapter 5 Partial preferential chromosome pairing is genotype dependent in tetraploid rose 109 Chapter 6 polymapR - linkage analysis and genetic map construction from F1 populations of outcrossing polyploids 137 Chapter 7 An ultra-dense integrated linkage map for hexaploid chrysanthemum enables multi-allelic QTL analysis 153 Chapter 8 Quantifying the power and precision of QTL analysis in autopolyploids under bivalent and multivalent genetic models 177 Chapter 9 Multi-environment QTL analysis of plant and flower morphological traits in tetraploid rose 209 Chapter 10 polyqtlR – an R package to analyse quantitative trait loci in autopolyploid populations 233 Chapter 11 General Discussion 255 References 277 Summary 297 Acknowledgements 299 About the author 302 List of publications 303 Education certificate 304 Chapter 1 General Introduction 7 ___________________________________________________________________________________General introduction Molecular markers and Mendel’s missing caveat It is only relatively recently that the terms “marker” and “molecular marker” have been taken to be synonymous. In his pioneering experiments with peas, Mendel was already studying the transmission and inheritance of a now-famous set of genetic “markers” (Mendel, 1866), with the physical expression of seven different traits (what we term “phenotypes”) being the marker set itself. It took almost fifty years before it was realised that these morphological markers also represented specific locations on chromosomes which were either transmitted together (due to genetic linkage) or independently (due to lack of linkage) (Morgan, 1911). Curiously, Mendel had selected only unlinked traits for his study of peas (whether this was by accident or by design we do not know). His second law, the law of independent assortment, states that alleles of one gene sort into gametes independently of the alleles of another gene. However, because chromosomes and their connection to inheritance had not yet been discovered, Mendel missed one vital caveat to this law, namely that independence only occurs if such genes are located on separate chromosomes (or perhaps at opposite ends of a single long chromosome). Most of what follows in this thesis is based on this non-independent segregation of linked loci. One of the major milestones in genetics was the realisation that a collection of linked markers could be arranged in a linear fashion, with distances between their positions estimated from the counts of co-inherited markers (Sturtevant, 1913). In his demonstration of this fact using six linked morphological markers of the common fruit fly Drosophila melanogaster, Sturtevant created the world’s first genetic linkage map (Sturtevant, 1913;Van Ooijen and Jansen, 2013). Nowadays, we generally rely on DNA markers (a.k.a. molecular markers) to identify positions on chromosomes. In this thesis we exclusively present data on single nucleotide polymorphism (SNP) markers. These are nucleotide positions which generally differ in the individuals being screened and are usually selected to be “bi-allelic” (i.e. alternating between two possible nucleotides in the material under study). However, the methods we develop are general to any bi-allelic marker system for which marker “dosage” counts can be accurately estimated. The term “dosage” is less commonly used in diploid studies, but is a very important concept in genetic analyses of polyploids. Dosage is generally understood to be the number of copies of the alternative allele carried by an individual at a particular locus. An illustration of the possible marker dosage scores in a tetraploid and hexaploid are shown in Figure 1. 8 ___________________________________________________________________________________Chapter 1 Linkage mapping and QTL analysis – part I The principal aim of this thesis is the development and exploration of methods and tools to create linkage maps and perform quantitative trait locus (QTL) analysis in polyploids. Both of these activities combined can conveniently be termed “genetic mapping” as the title of this thesis suggests. These are not new activities – as already mentioned, the first linkage map was constructed in 1913, and the first QTL analysis was arguably conducted a decade later (Sax, 1923). The novelty of this work lies in its application to polyploids, a group of organisms that possess much more complex genomes than their diploid counterparts, and in its use of modern genotyping data which often consists of many tens of thousands of markers. a. 0 1 2 3 4 b. 0 1 2 3 4 5 6 Figure 1. Representation of the possible marker dosage scores, for a. Tetraploid (ploidy = 4) and b. Hexaploid (ploidy = 6). In general, there are ploidy + 1 possible dosage classes at a bi- allelic marker position, here shown in blue / red. The convention for assigning dosage scores is to count the number of copies of the alternative allele (coloured red), with the reference allele count (in blue) given by ploidy – dosage. Modern plant and animal breeding has benefitted from the use of molecular markers, allowing specific traits of interest to be predicted without having to necessarily grow a plant to maturity and test the trait directly. This can have many advantages, for example by allowing a greater number of traits to be more cost-effectively combined, allowing selection among multiple progenies, or in material for which phenotyping is difficult 9 ___________________________________________________________________________________General introduction or expensive etc. At least, that is the intention of marker-assisted selection (MAS). In practice, MAS has met with mixed success in plant breeding programs (Collard and Mackill, 2008;Hospital, 2009). In the autotetraploid crop potato (Solanum tuberosum L.), markers have been demonstrated to be useful for certain disease resistances (e.g. potato cyst nematode (Schultz et al., 2012)) and have been shown to be a cost-effective proposition if deployed appropriately in a breeding program (Slater et al., 2013). However, in order to use markers effectively, we need to develop models to capture the relationship between a plant’s genotype and its phenotype. For polyploids, modelling these
Load more

Recommended publications
  • HAPLOID SELECTION for LOW TEMPERATURE TOLERANCE of TOMATO POLLEN LANTS Alternate Regularly Between the Sporophytic and Gametophy
    HAPLOID SELECTION FOR LOW TEMPERATURE TOLERANCE OF TOMATO POLLEN DANIEL ZAMIR,1 STEVEN D. TANKSLEYZ AND RICHARD A. JONES Department of Vegetable Crops, University of California, Davis, CA95616 Manuscript received May 16, 1981 Revised copy accepted February 16, 1982 ABSTRACT Pollen grains were harvested from an interspecific F, hybrid between the cultivated tomato, Lycopersicon esculenturn Mill., and its wild relative Lycopersicon hirsutum Humb. & Bonpl., a low temperature tolerant accession originating from an altitude of 3200 m in the Peruvian Andes. The two species differ for electrophoretically-detectable loci that mark six (possibly seven) of the 12 tomato chromosomes. Isozyme analysis of the BC, populations derived from controlled pollinations at normal and low temperatures indicates a sig- nificant skewing of allelic frequencies favoring two independent chromosome segments of L. hirsutum at low temperatures. The results demonstrate that gametophytic selection for low temperature tolerance of tomato pollen is determined, at least in part, by genes expressed in the haploid pollen. LANTS alternate regularly between the sporophytic and gametophytic phases Ip of their life cycles. During the evolution of higher plants the gametophytic phase was dramatically reduced both in physical dimensions and in the rela- tive time it occupied in the life cycle. This may explain why genetic research has been primarily devoted to the prominent sporophytic phase. In a unique study, CLEGG,KAHLER and ALLARD(1978) examined an experimental barley population for selection at different stages of the life cycle. Estimates were ob- tained for viability (zygote to adult) and fertility (adult to zygote) components of selection associated with electrophoretically detectable allozymes.
    [Show full text]
  • Selective Embryo Abortion Hypothesis Revisited a Molecular Approach
    298 Review Article Selective Embryo Abortion Hypothesis Revisited ± A Molecular Approach G. Korbecka, P. G. L. Klinkhamer, and K. Vrieling Institute of Evolutionary and Ecological Sciences, Section Plant Ecology, Leiden, The Netherlands Received: October 9, 2001; Accepted: February 20, 2002 Abstract: Many plant species abort a large fraction of their em- otypes with a potential low quality later in life such that an in- bryos. It has often been suggested that embryos of genotypes crease in the level of abortion leads to an increase in offspring that would perform worse later in life are preferentially abort- quality. In evolutionary theory the hypothesis is important in ed. Such selective embryo abortion would lead to investment relation to explanations for low seed to ovule ratios and the of resources only in the offspring with the highest potential fit- optimal allocation of resources to male and female reproduc- ness. Many studies have shown that otherwise viable embryos tion in hermaphroditic plants. are aborted. However, only few manipulative studies have in- deed shown a correlation between the level of abortion and The SEA hypothesis is based on the following premises: i) offspring quality and these studies have been challenged for plants abort a substantial part of the embryos, ii) otherwise their experimental design. Molecular techniques open new op- viable embryos are aborted, iii) the probability of being abort- portunities to study selective embryo abortion. Non-random ed depends on the genotype of the embryo. In contrast to abortion at the level of molecular markers can be observed as a ample theoretical attention given to the SEA hypothesis e.g., deviation from Mendelian segregation: over- or under-repre- Kozøowski and Stearns, 1989[56]; Latta, 1995[61]; Burd, 1998[16]), sentation of markers in the offspring.
    [Show full text]
  • Environmental Influence on Primary Sex Ratio in a Dioecious Plant
    Environmental influence on primary sex ratio in a dioecious plant Ivana Stehlik, Jannice Friedman, and Spencer C. H. Barrett* Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, Canada M5S 3B2 Edited by May R. Berenbaum, University of Illinois at Urbana–Champaign, Urbana, IL, and approved May 16, 2008 (received for review February 27, 2008) The proximity of mates can influence mating opportunities and the species are generally more plastic than animals in gender ex- quantity and quality of offspring, especially in dioecious plant pression, they typically show environmentally influenced sex- species. Progeny sex ratios modulated by environmental condi- allocation plasticity or sex inconstancy during flowering (15–17). tions is one of the most radical ways in which offspring quality may Evidence for environmental sex determination early in devel- be influenced, yet it has rarely been reported in plants. A mecha- opment is relatively rare in seed plants (e.g., Spinacia oleracea: nism proposed to influence progeny sex ratios in dioecious plants ref. 18), and how frequent environmental influences interact involves competition between female- and male-determining mi- with genetic sex determination mechanisms to influence progeny crogametophytes (certation) as a result of variation in pollination sex ratios is unclear. intensity. However, the role of selective fertilization in dioecious In the dioecious herb Rumex nivalis (Polygonaceae), sex plants is controversial and has not been demonstrated under field determination is governed by heteromorphic sex chromosomes conditions. Here we investigate whether natural variation in the with females homogametic XX and males heterogametic XY1Y2 spatial arrangement of females and males influences pollination (19, 20).
    [Show full text]
  • Floral Traits Influence the Opportunity for Selection Among Male Gametophytes: Independent and Combined Effects of Style Length and Petal Area
    RESEARCH ARTICLE BRIEF COMMUNICATION Floral traits influence the opportunity for selection among male gametophytes: independent and combined effects of style length and petal area Susan J. Mazer1,2 , Joseph P. Chellew1, and Kristen Peach1 Manuscript received 14 December 2018; revision accepted 31 January PREMISE: Strong correlations between traits can obscure their independent effects on 2019. components of reproduction. Style length (SL) and petal area (PA) vary within species, for 1 Department of Ecology, Evolution, and Marine Biology, University example, but their independent effects on the opportunity for selection among pollen of California, Santa Barbara, Santa Barbara, California 93106, USA genotypes are poorly understood. Previous work in Clarkia detected a positive effect of 2 Author for correspondence (e-mail: [email protected]) SL on pollen receipt, potentially intensifying selection. However, this apparent effect of Citation: Mazer, S. J., J. P. Chellew, and K. Peach. 2019. Floral traits SL may be influenced by a correlated trait, such as PA. Here, we examine the independent influence the opportunity for selection among male gametophytes: inde- pendent and combined effects of style length and petal area. American effects of these two traits on pollen receipt and performance. Journal of Botany 106(5): 744–753. METHODS: We collected petals and styles from wild populations of two insect- pollinated doi:10.1002/ajb2.1274 Clarkia taxa and estimated the independent and combined effects of SL and PA on pollen receipt and performance. RESULTS: In both taxa, SL and PA are positively correlated. In C. unguiculata, both traits positively and independently affect pollen receipt, but in C. xantiana ssp.
    [Show full text]
  • Lessons from Holocentric Chromosomes
    Downloaded from genesdev.cshlp.org on September 23, 2021 - Published by Cold Spring Harbor Laboratory Press REVIEW Coordinating cohesion, co-orientation, and congression during meiosis: lessons from holocentric chromosomes Mara Schvarzstein, Sarah M. Wignall, and Anne M. Villeneuve1 Department of Developmental Biology, Stanford University School of Medicine, Stanford, California 94305, USA; and Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA Organisms that reproduce sexually must reduce their release of chiasmata and reductional segregation in mei- chromosome number by half during meiosis to generate osis I, while retaining a local region of sister cohesion haploid gametes. To achieve this reduction in ploidy, necessary to align chromosomes and to maintain sister organisms must devise strategies to couple sister chro- connections until anaphase of meiosis II. (2) Sister chro- matids so that they stay together during the first meiotic matids must be temporarily ‘‘co-oriented’’ during meiosis division (when homologous chromosomes separate) and I, so that they move together to the same spindle pole. then segregate away from one another during the sec- Sister chromatids must then switch their behavior, be- ond division. Here we review recent findings that shed coming ‘‘bioriented’’ on the meiosis II spindle so that they light on how Caenorhabditis elegans, an organism with can move apart toward opposite spindle poles. holocentric chromosomes, deals with these challenges In organisms with monocentric chromosomes, the of meiosis by differentiating distinct chromosomal sub- single localized centromere serves as the focal point for domains and remodeling chromosome structure during mechanisms that serve to co-orient sister chromatids at prophase.
    [Show full text]
  • The Advantages and Disadvantages of Being Polyploid
    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 Polyploidy is the heritable condition of possessing that these processes are often not random and that the A polyploid that has been more than two complete sets of chromosomes. Most function and properties of the encoded protein affect produced by artificially polyploids have an even number of sets of chromo- the outcome18–25. By providing duplicated genes, poly- inducing chromosome somes, with four being the most common (tetraploidy). ploidization might fuel long-term diversification and doubling. Polyploids are very common among plants and com- evolutionary success. DIPLOIDIZATION mon among fish and amphibians, and are usually fit and In this review I discuss possible advantages of Gradual conversion from well adapted. Indeed, the study of eukaryotic genomes polyploidy and constraints on polyploid formation polyploidy to diploidy through is providing surprising proof of the evolutionary poten- that are indicated by either experimental evidence or genetic changes that tial of polyploids: many sequenced genomes display theoretical considerations.
    [Show full text]
  • Varietal Variation and Chromosome Behaviour During Meiosis in Solanum Tuberosum
    Heredity (2020) 125:212–226 https://doi.org/10.1038/s41437-020-0328-6 ARTICLE Varietal variation and chromosome behaviour during meiosis in Solanum tuberosum 1 1 1 1 2 1 Anushree Choudhary ● Liam Wright ● Olga Ponce ● Jing Chen ● Ankush Prashar ● Eugenio Sanchez-Moran ● 1,3 1 Zewei Luo ● Lindsey Compton Received: 16 December 2019 / Revised: 2 June 2020 / Accepted: 2 June 2020 / Published online: 10 June 2020 © The Author(s) 2020. This article is published with open access Abstract Naturally occurring autopolyploid species, such as the autotetraploid potato Solanum tuberosum, face a variety of challenges during meiosis. These include proper pairing, recombination and correct segregation of multiple homologous chromosomes, which can form complex multivalent configurations at metaphase I, and in turn alter allelic segregation ratios through double reduction. Here, we present a reference map of meiotic stages in diploid and tetraploid S. tuberosum using fluorescence in situ hybridisation (FISH) to differentiate individual meiotic chromosomes 1 and 2. A diploid-like behaviour at metaphase I involving bivalent configurations was predominant in all three tetraploid varieties. The crossover frequency per bivalent fi 1234567890();,: 1234567890();,: was signi cantly reduced in the tetraploids compared with a diploid variety, which likely indicates meiotic adaptation to the autotetraploid state. Nevertheless, bivalents were accompanied by a substantial frequency of multivalents, which varied by variety and by chromosome (7–48%). We identified possible sites of synaptic partner switching, leading to multivalent formation, and found potential defects in the polymerisation and/or maintenance of the synaptonemal complex in tetraploids. These findings demonstrate the rise of S. tuberosum as a model for autotetraploid meiotic recombination research and highlight constraints on meiotic chromosome configurations and chiasma frequencies as an important feature of an evolved autotetraploid meiosis.
    [Show full text]
  • Fisiologia Vegetal
    IN VITRO PRESERVATION AND MANIPULATION OF POLLEN VIABILITYS H O R T C O M M U N I C A T I O65 N Pollen treatment in high osmotic potential: a simple tool for in vitro preservation and manipulation of viability in gametophytic populations Leandro Lopes Loguercio Departamento de Ciências Biológicas - DCB, Universidade Estadual de Santa Cruz, Rod. Ilhéus-Itabuna, Km 16, Ilhéus, BA, 45650-000, Brasil; E-mail: [email protected] A method for in vitro preservation and manipulation of pollen viability based on simple changes in osmotic potential (sucrose concentrations) in culture media was developed using tobacco pollen as the experimental model. High osmotic potentials were capable of reversibly inhibiting pollen germination, preserving its viability at room temperature for long periods, as assessed by subsequent incubation in germination medium. When pollen was pre-germinated for different periods and subsequently incubated in 80 % sucrose medium (inhibiting medium) there was a progressive decrease in its viability, which was a trend best described by a quadratic regression line. Nevertheless, very small variations in pollen- tube lengths and viable pollen grains more resistant to the pre-germination step were detected by this procedure. Conse- quences and potential applications of these findings were discussed for use in analyses of variability, selection in gameto- phytic populations and pollen storage. Key words: Gametophytic selection, in vitro pollen germination, Nicotiana tabacum, pollen storage, pollen viability. Tratamento de pólen em osmolaridade elevada: técnica simples para preservação e manipulação in vitro da viabili- dade de populações de gametófitos: Um método para a preservação e manipulação da fisiologia de germinação de pólen foi desenvolvido com base em meras variações na osmolaridade dos meios de cultura, utilizando pólen de tabaco como modelo experimental.
    [Show full text]
  • Pollen Competition Reduces Inbreeding Depression in Collinsia Heterophylla (Plantaginaceae)
    doi:10.1111/j.1420-9101.2006.01233.x Pollen competition reduces inbreeding depression in Collinsia heterophylla (Plantaginaceae) A˚ .LANKINEN*, & W. S. ARMBRUSTER*,à,§ *Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway Department of Plant Ecology and Systematics, Lund University, Ecology Building, Lund, Sweden àInstitute of Arctic Biology and Department of Biology and Wildlife, University of Alaska, Fairbanks, AK, USA §School of Biological Sciences, University of Portsmouth, King Henry Building, Portsmouth, UK Keywords: Abstract mating-system evolution; We tested two predictions of the hypothesis that competition between self- mixed-mating system; pollen may mitigate negative genetic effects of inbreeding in plants: (1) intense pollen-load size; competition among self-pollen increases offspring fitness; and (2) pollen prezygotic selection; competition reduces the measured strength of inbreeding depression. We used self-pollination. Collinsia heterophylla (Plantaginaceae), an annual with a mixed mating system, to perform controlled crosses in which we varied both the size of the pollen load and the source of pollen (self vs. outcross). Fitness of selfed offspring was higher in the high pollen-load treatment. Our second prediction was also upheld: inbreeding depression was, on average, lower when large pollen loads were applied (11%) relative to the low pollen-load treatment (28%). The reduction was significant for two fitness components relatively late in the life- cycle: number of surviving seedlings and pollen-tube growth rate in vitro. These findings suggest that intermittent inbreeding, which leads to self- fertilization in plants with genetic loads, may select for traits that enhance pollen competition. phytes (Mulcahy et al. 1992; Walsh & Charlesworth Introduction 1992; Hormaza & Herrero 1994, 1996).
    [Show full text]
  • Gametophytic Selection: a Simple Technique for Thermo Tolerance Genotypes Identification in Maize
    Int.J.Curr.Microbiol.App.Sci (2017) 6(8): 1649-1655 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 8 (2017) pp. 1649-1655 Journal homepage: http://www.ijcmas.com Review Article https://doi.org/10.20546/ijcmas.2017.608.198 Gametophytic Selection: A Simple Technique for Thermo Tolerance Genotypes Identification in Maize Ashutosh Singh1*, Rajen Chowdhury2 and Ratan Das3 1Department of Plant Biotechnology UAS GKVK Bengaluru, India 2Department of Biotechnology, CPMB&B, Tamil Nadu Agricultural University, India 3Department of Horticulture and Post Harvest Technology Visva-Bharati, India *Corresponding author: ABSTRACT K e yw or ds Temperature of environment increase day by day so present time identification of Thermo tolerance heat tolerant genotypes is great challenge. Because tolerance to high temperature Genotypes, is a multi-genic character and also many screenable traits are available. But there no single techniques available which give holistic idea about plant level heat Gametophytic selection . tolerance. Gametophytic selection could be one of the alternative strategies. There are many successful attempt have been made to improve the crop plants by Article Info gametophytic selection. In this review discuss the advantages of gametophytic Accepted: selection over sporophytic selection, the effect of high temperature on maize and 17 June 2017 how gametophytic selection is a potential option for high temperature screening in Available Online: 10 August 2017 maize. Introduction The main goal of any plant breeding program are developed a small but growing resurgence is the improvement of all characteristics that of research focused on male gamete selection contribute to economic value.
    [Show full text]
  • The Distribution of Crossovers, and the Measure of Total Recombination
    bioRxiv preprint doi: https://doi.org/10.1101/194837; this version posted September 27, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. The distribution of crossovers, and the measure of total recombination Carl Veller∗;y;1 Martin A. Nowak∗;y;z Abstract Comparisons of genetic recombination, whether across species, the sexes, individ- uals, or different chromosomes, require a measure of total recombination. Traditional measures, such as map length, crossover frequency, and the recombination index, are not influenced by the positions of crossovers along chromosomes. Intuitively, though, a crossover in the middle of a chromosome causes more recombination than a crossover at the tip. Similarly, two crossovers very close to each other cause less recombination than if they were evenly spaced. Here, we study a measure of total recombination that does account for crossover position: average r, the probability that a random pair of loci recombines in the production of a gamete. Consistent with intuition, average r is larger when crossovers are more evenly spaced. We show that aver- age r can be decomposed into distinct components deriving from intra-chromosomal recombination (crossing over) and inter-chromosomal recombination (independent as- sortment of chromosomes), allowing separate analysis of these components. Average r can be calculated given knowledge of crossover positions either at meiosis I or in gametes/offspring. Technological advances in cytology and sequencing over the past two decades make calculation of average r possible, and we demonstrate its calculation for male and female humans using both kinds of data.
    [Show full text]
  • Toward the Evolutionary Genomics of Gametophytic
    ORIGINAL ARTICLE doi:10.1111/j.1558-5646.2008.00475.x TOWARD THE EVOLUTIONARY GENOMICS OF GAMETOPHYTIC DIVERGENCE: PATTERNS OF TRANSMISSION RATIO DISTORTION IN MONKEYFLOWER (MIMULUS) HYBRIDS REVEAL A COMPLEX GENETIC BASIS FOR CONSPECIFIC POLLEN PRECEDENCE Lila Fishman,1,2 Jan Aagaard,3,4 and John C. Tuthill1,5 1Division of Biological Sciences, HS104, University of Montana, Missoula, Montana 59812 2E-mail: lfi[email protected] 3Department of Genome Sciences, University of Washington, Seattle, Washington 98195 4E-mail: [email protected] 5E-mail: [email protected] Received April 11, 2008 Accepted June 27, 2008 Conspecific pollen precedence (CPP) is a major component of reproductive isolation between many flowering plant taxa and may reveal mechanisms of gametophytic evolution within species, but little is known about the genetic basis and evolutionary history of CPP. We systematically investigated the genetic architecture of CPP using patterns of transmission ratio distortion (TRD) in F2 and backcross hybrids between closely related species of Mimulus (Phrymaceae) with divergent mating systems. We found that CPP in Mimulus hybrids was polygenic and was the majority source of interspecific TRD genome-wide, with at least eight genomic regions contributing to the transmission advantage of M. guttatus pollen grains on M. guttatus styles. In aggregate, these male-specific transmission ratio distorting loci (TRDLs) were more than sufficient to account for the 100% precedence of pure M. guttatus pollen over M. nasutus pollen in mixed pollinations of M. guttatus. All but one of these pollen TRDLs were style- dependent; that is, we observed pollen TRD in F1 and/or M.
    [Show full text]