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Selective Embryo Abortion
Selective embryo abortion (also known as selective seed abortion and selective ovule abortion ), is a form of non-random, premature termination of embryonic development in plants. Selective embryo abortion assumes that embryo termination depends on the genetic quality of seeds developing within an ovary, and predicts that successfully matured seeds will be of greater fitness than aborted seeds. Consequently, selective embryo abortion has the potential to act as a unique stage of natural selection, influencing the evolution of plant populations and species. This concept was described by botanist John T. Buchholz in 1922 under his framework of developmental selection, which referred to selective embryo abortion as “interovular selection.” Selective embryo abortion may result from competition among embryos for maternal resources. The maternal plant may also play an active role by recognizing and selectively aborting genetically inferior embryos. Evidence of offspring fitness ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with selective breeding, artificial selection, which in his view is intentional, whereas natural selection is not. Genetic diversity, Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits. The environment of a genome includes the molecular biology in the Cell (biology), cell, other cells, other individuals, populations, species, as well as the abiotic environment. Because individuals with certain variants of the trait tend ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Theodore Buchholz
John Theodore Buchholz (1888–1951) was an American botanist, specialising in gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...s. ;Selected bibliography *Polyembryony among Abietineae. ''Bot. Gaz''. 69: 153-167 (1920). *Embryo development and polyembryony in relation to the phylogeny of conifers. ''Amer. J. Bot''. 7: 125-145 (1920). *The classification of Coniferales. ''Trans. Illinois State Acad. Sci''. 25: 112–113. (1933). *The generic segregation of the Sequoias. ''Amer. J. Bot''. 26: 535-538 (1939). *A comparison of the embryogeny of Picea and Abies. ''Madroño'' 6: 156-167 (1942). *Generic and subgeneric distribution of the Coniferales. ''Bot. Gaz''. 110: 80-91 (1948). *Additions to the coniferous flora of New Caledonia. ''Bull. Mus. Hist. Nat.'' (Paris) sér.2, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Developmental Selection
Developmental selection is selection that occurs on developmental units in an organism, such as cell lineages, embryos, and gametes or gametophytes. Generally, developmental selection is differentiated from natural selection because the targets of selection are internal to an organism contain the developmental units, rather than selection due to external environmental factors that favor specific phenotypes. However, in animals, developmental selection against offspring can manifest in the external environment, in which parents might select against offspring with developmental instabilities, or when offspring with deleterious malformations may not survive. Developmental selection in plants Selective embryo abortion A common form of developmental selection in plants is selective ovule abortion, where the maternal parent selects against unstable embryos. Abortion of low-viability offspring may be driven by either genetic factors or environmental stress. Developmental selection may ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-incompatibility
Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporally (dichogamy) separation. SI is best-studied and particularly common in flowering plants, although it is present in other groups, including sea squirts and fungi. In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a matching allele or genotype, the process of pollen germination, pollen-tube growth, ovule fertilization, or embryo development is inhibited, and consequently no seeds are produced. SI is one of the most important means of preventing inbreeding and promoting the generation of new genotypes in plants and it is considered one of the causes of the spread and success of angiosperms on Earth. Mechan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gametophytic Selection
Gametophytic selection is the selection of one haploid pollen grain over another through the means of pollen competition (see also certation), and that resulting sporophytic generations are positively affected by this competition. Evidence for the positive effects of gametophytic selection on the sporophyte generation has been observed in several flowering plant species, but there are is still some debate as to the biological significance of gametophytic selection. Non-random success of pollen tubes Pollen competition hypothesis The competitive ability of pollen grains ( microgapmetophytes) is rooted in the expression of their haploid genomes. The haploid genes are expressed immediately after pollen development and during pollen germination and pollen-tube growth. About 60% of genes expressed in the sporophyte are also expressed in the microgametophyte. This expression influences the ability of pollen tubes to compete during growth. When pollen competition occurs, the competi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inbreeding Depression
Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding (the breeding of related individuals). Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. Inbreeding depression is often the result of a population bottleneck. In general, the higher the genetic variation or gene pool within a breeding population, the less likely it is to suffer from inbreeding depression, though inbreeding and outbreeding depression can simultaneously occur. Inbreeding depression seems to be present in most groups of organisms, but varies across mating systems. Hermaphroditic species often exhibit lower degrees of inbreeding depression than outcrossing species, as repeated generations of selfing is thought to purge deleterious alleles from populations. For example, the outcrossing nematode (roundworm) ''Caenorhabditis remanei'' has been demonstrated to suffer severely from inbreeding depression, unlike its he ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inbreeding
Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity. Animals avoid incest only rarely. Inbreeding results in homozygosity, which can increase the chances of offspring being affected by recessive traits. In extreme cases, this usually leads to at least temporarily decreased biological fitness of a population (called inbreeding depression), which is its ability to survive and reproduce. An individual who inherits such deleterious traits is colloquially referred to as ''inbred''. The avoidance of expression of such deleterious recessive alleles caused by inbreeding, via inbreeding avoidance mechanisms, is the main selective reason for outcrossin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Load
Genetic load is the difference between the fitness of an average genotype in a population and the fitness of some reference genotype, which may be either the best present in a population, or may be the theoretically optimal genotype. The average individual taken from a population with a low genetic load will generally, when grown in the same conditions, have more surviving offspring than the average individual from a population with a high genetic load. Genetic load can also be seen as reduced fitness at the population level compared to what the population would have if all individuals had the reference high-fitness genotype. High genetic load may put a population in danger of extinction. Fundamentals Consider n genotypes \mathbf _1, \dots, \mathbf _n, which have the fitnesses w_1, \dots, w_n and frequencies p_1, \dots, p_n, respectively. Ignoring frequency-dependent selection, the genetic load L may be calculated as: :L = where w_\max is either some theoretical optimum, or t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
