Sex Mechanism in Coccinia indica Wight and Arn.
TL;DR: The present note is based on the results of a critical cytological investigation of different sex types, such as the diploid male and female, the gynodiœcious form and a triploids male of C. indica.
Abstract: SOME of the diœcious species of Cucurbitaceae have been cytologically investigated by several previous workers to ascertain whether the morphological differences in flowers between the sexes could be correlated with any observable chromosomal differences of their gametes. So far, only two species among members of this family, namely, Trichosanthes japonica1–3 and Coccinia indica4–6 have been found to possess well-defined sex-chromosomes. In T. japonica, the male is reported to be the heterogametic sex, whereas in C. indica contrary evidences have been furnished by Kumar and Deodikar6 and Bhaduri and Bose4. The present note is based on the results of a critical cytological investigation of different sex types, such as the diploid male and female, the gynodiœcious form and a triploid male of C. indica.
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TL;DR: In plants it is possible to follow both the evolution of dioecism from hermaphroditism (or monoecism) and the reverse process, and in many cases, better tools for studying the genetics of sex determination thandioecious animals.
Abstract: Publisher Summary Dioecism has arisen independently in different plant families and plant genera. In the majority of cases, the evolution of dioecism has apparently taken place on the species level; in some cases, on the subgeneric level (rumex) or generic level (humulus). Few families (salicaceae) comprise only dioecious species. Dioecious plants offer, in many cases, better tools for studying the genetics of sex determination than dioecious animals. First, the fact that dioecious plants have arisen independently gives an opportunity to study the different ways in which dioecism may become established. Second, in plants the step from dioecism to bisexuality is often a short one and in most cases, dioecism is not clear-cut. In many dioecious species (e.g. mercurialis), bisexual types are found in nature often with a rather high frequency. Such bisexual individuals of normally dioecious plant species are almost always fertile and can be genetically studied, whereas similar bisexual animals are sterile intersexes. In plants it is possible to follow both the evolution of dioecism from hermaphroditism (or monoecism) and the reverse process.
638 citations
TL;DR: Sex chromosomes in land plants can evolve as a consequence of close linkage between the two sex determination genes with complementary dominance required to establish stable dioecious populations, and they are found in at least 48 species across 20 families.
Abstract: Sex chromosomes in land plants can evolve as a consequence of close linkage between the two sex determination genes with complementary dominance required to establish stable dioecious populations, and they are found in at least 48 species across 20 families. The sex chromosomes in hepatics, mosses, and gymnosperms are morphologically heteromorphic. In angiosperms, heteromorphic sex chromosomes are found in at least 19 species from 4 families, while homomorphic sex chromosomes occur in 20 species from 13 families. The prevalence of the XY system found in 44 out of 48 species may reflect the predominance of the evolutionary pathway from gynodioecy towards dioecy. All dioecious species have the potential to evolve sex chromosomes, and reversions back from dioecy to various forms of monoecy, gynodioecy, or androdioecy have also occurred. Such reversals may occur especially during the early stages of sex chromosome evolution before the lethality of the YY (or WW) genotype is established.
393 citations
TL;DR: Comparative analysis of carefully selected plant species together with some fish species promises new insights into the origins of sex chromosomes and the selective forces driving their evolution.
Abstract: Sex chromosomes in dioecious and polygamous plants evolved as a mechanism for ensuring outcrossing to increase genetic variation in the offspring. Sex specificity has evolved in 75% of plant families by male sterile or female sterile mutations, but well-defined heteromorphic sex chromosomes are known in only four plant families. A pivotal event in sex chromosome evolution, suppression of recombination at the sex determination locus and its neighboring regions, might be lacking in most dioecious species. However, once recombination is suppressed around the sex determination region, an incipient Y chromosome starts to differentiate by accumulating deleterious mutations, transposable element insertions, chromosomal rearrangements, and selection for male-specific alleles. Some plant species have recently evolved homomorphic sex chromosomes near the inception of this evolutionary process, while a few other species have sufficiently diverged heteromorphic sex chromosomes. Comparative analysis of carefully selected plant species together with some fish species promises new insights into the origins of sex chromosomes and the selective forces driving their evolution.
117 citations
TL;DR: A PCR-based Seedling Sex Diagnostic Assay (SSDA) specially designed for early sexing of papaya seedlings is reported here and could be easily applied to molecular analysis of any agriculturally important trait for which specific DNA probes could be identified and hence opens new avenues of research in the field of genetic diagnostics of plants.
Abstract: Female plants of several dioecious angiosperms are commercially valued for production of fruits or seeds, viz. papaya, nutmeg, pistachio, kiwi fruit and jojoba. To make the cultivation profitable it is necessary to grow more female than male plants. To discriminate between male and female plants, sex-specific molecular markers have been identified in a few dioecious species such as Silene and pistachio. However, accurate and convenient sex diagnostic methods for early sexing of seedlings are not available to date. For the first time, we report here a PCR-based Seedling Sex Diagnostic Assay (SSDA) specially designed for early sexing of papaya seedlings. We have developed a male-specific SCAR marker in papaya by cloning a male-specific RAPD (831 bp) fragment and designing longer primers. The potential of this SCAR marker is further exploited to develop a simplified and highly accurate sex diagnostic assay by (1) including an internal PCR control, (2) following a single-step DNA extraction procedure and (3) optimising the PCR conditions to simultaneously amplify male-specific and control bands from the crude leaf extract. This diagnostic approach would be of great commercial significance to papaya growers as well as to seed companies and plant nurseries for early identification of female seedlings of dioecious species. In principle, this experimental design could be easily applied to molecular analysis of any agriculturally important trait for which specific DNA probes could be identified and hence opens new avenues of research in the field of genetic diagnostics of plants.
92 citations
Cites background from "Sex Mechanism in Coccinia indica Wi..."
...A few dioecious plants likeSilene[14], Rumex[4], Humulus[17] andCoccinia [10] possess distinct sex chromosomes and thus the sex of these plants can be distinguished cytologically....
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TL;DR: Dioecious plants have unisexual flowers, which have stamens or pistils, which are caused by the suppression of opposite sex primordia, and sex chromosome linkage in these plants suggests that female suppressor and stamen promoter genes are localized on the Y chromosome.
Abstract: Sex chromosomes have been reported in several dioecious plants. The most general system of sex determination with sex chromosomes is the XY system, in which males are the heterogametic sex and females are homogametic. Genetic systems in sex determination are divided into two classes including an X chromosome counting system and an active Y chromosome system. Dioecious plants have unisexual flowers, which have stamens or pistils. The development of unisexual flowers is caused by the suppression of opposite sex primordia. The expression of floral organ identity genes is different between male and female flower primordia. However, these floral organ identity genes show no evidence of sex chromosome linkage. The Y chromosome of Rumex acetosa contains Y chromosome-specific repetitive sequences, whereas the Y chromosome of Silene latifolia has not accumulated chromosome-specific repetitive sequences. The different degree of Y chromosome degeneration may reflect on evolutionary time since the origination of dioecy. The Y chromosome of S. latifolia functions in suppression of female development and initiation and completion of anther development. Analyses of mutants suggested that female suppressor and stamen promoter genes are localized on the Y chromosome. Recently, some sex chromosome-linked genes were isolated from flower buds of S. latifolia.
79 citations
References
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TL;DR: Are sex chromosomes in higher pl,~nt~ nucleologenic?
Abstract: Introduction . M~t~rial and methods 0 bservations: Cucumis a~giz,u~ . Cucumis Memo Trichoaanth~ diolca Luffa aegyp~i~c,a . Luffa a~u~an~u~a . 6'o~iuia indica Beuincasa cerifera M~,mrdica cllarantia Cucurbita ~r~aarima Polysomaty Discussion (i) Numerica! correlation between m a~m um number ofnucleoli, sat~llltes and secondary constrictions (ii) Maximum number of nucleo]i ,lnd nucleolar constrictions of chromosomes witah reference to polyplcidy and aneuploidy . . . {iii) Variation of chromosome number in Cucm.bitaceac and R~. cytogsnetic interpretation (iv} Are sex chromosomes in higher pl,~nt~ nucleologenic? . Summary P, efsrsnces P A G ~
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39 citations
TL;DR: In this article, the exact circumstances of chromosome distribution in the division of the pollen-mother-cell nuclei of certain dioecious angiosperms were investigated with the purpose of determining the exact conditions of chromosome distributions in order to detect any morphological differences between members of a pair that might be correlated with the usually diospermic condition of these species.
Abstract: The cytological investigations reported in the present paper were undertaken with the purpose of determining the exact circumstances of chromosome distribution in the division of the pollen-mother-cell nuclei of certain dioecious angiosperms. Attention has been focused on the stages of the heterotypic division in which the "homologous" chromosomes pair and separate, in order to detect any morphological difference between members of a pair that might be correlated with the usually dioecious condition of these species. No good evidence of such a difference has been found in Bryonia dioica L., Clematis virginiana L., Smilax herbacea L., Menispermum canadense L., or Carica papaya L., while the conspicuous heterochromosome pair of Lychnis cdlba Mill. (Melandrium album L.), already described by investigators in England, Sweden, and Germany, has been identified in material collected in the neighborhood of Madison, Wisconsin. A preliminary report has already been made of some of the results of the present work (Lindsay, 1929).
35 citations
01 Jan 1928
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