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Sex is the trait that determines whether a sexually reproducing animal or plant produces male gametes or female ones. Male plants and animals produce smaller gametes while females produce larger ones. Organisms that produce both types of gametes are called hermaphrodites. During sexual reproduction, male and female gametes fuse to form zygotes, which develop into offspring that inherit traits from each parent.
Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally called fertilisation. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and the second recessive. This state of having two different variants of the same gene on each chromosome is originally caused by a mutation in one of the genes, either new or inherited. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes (autosomes) and their associated traits, while those on sex chromosomes (allosomes) are termed X-linked dominant, X-linked recessive or Y-linked; these have an inheritance and presentation pattern that depends on the sex of both the parent and the child. Since there is only one copy of the Y chromosome, Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance such as incomplete dominance, in which a gene variant has a partial effect compared to when it is present on both chromosomes, and co-dominance, in which different variants on each chromosome both show their associated traits.
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, and bats; water; wind; and even plants themselves, when self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species it can produce hybrid offspring in nature and in plant breeding work.
Self-pollination is a form of pollination in which pollen from the same plant arrives at the stigma of a flower or at the ovule. There are two types of self-pollination: in autogamy, pollen is transferred to the stigma of the same flower; in geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm. Some plants have mechanisms that ensure autogamy, such as flowers that do not open (cleistogamy), or stamens that move to come into contact with the stigma. The term selfing that is often used as a synonym, is not limited to self-pollination, but also applies to other types of self-fertilization.
The sex ratio is the ratio of males to females in a population. The ratio tends to be 1:1 in most sexually reproducing species, which is explained by Fisher's principle. Many species deviate from an even sex ratio, either periodically or permanently. Examples include parthenogenic species, periodically mating organisms such as aphids, some eusocial wasps, bees, ants, and termites.
Plant reproductive morphology is the study of the physical form and structure of those parts of plants directly or indirectly concerned with sexual reproduction.
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 temporal (dichogamy) separation.
In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric.
Sequential hermaphroditism is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, a sequential hermaphrodite produces eggs and sperm at different stages in life. Species that can undergo these changes from one sex to another do so as a normal event within their reproductive cycle that is usually cued by either social structure or the achievement of a certain age or size.
Plant breeders use different methods depending on the mode of reproduction of crops, which include:
The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes (haploid) combines with another to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. Sexual reproduction does not occur in prokaryotes, but they have processes with similar effects such as bacterial conjugation, transformation and transduction, which may have been precursors to sexual reproduction in early eukaryotes.
Gynodioecy is a rare breeding system that is found in certain flowering plant species in which female and hermaphroditic plants coexist within a population. Gynodioecy is the evolutionary intermediate between hermaphroditism and dioecy.
Pollination traps or trap-flowers are plant flower structures that aid the trapping of insects, mainly flies, so as to enhance their effectiveness in pollination. The structures of pollination traps can include deep tubular corollas with downward pointing hairs, slippery surfaces, adhesive liquid, attractants, flower closing and other mechanisms.
Silene is a flowering plant genus that has evolved a dioecious reproductive system. This is made possible through heteromorphic sex chromosomes expressed as XY. Silene recently evolved sex chromosomes 5-10 million years ago and are widely used by geneticists and biologists to study the mechanisms of sex determination since they are one of only 39 species across 14 families of angiosperm that possess sex-determining genes. Silene are studied because of their ability to produce offspring with a plethora of reproductive systems. The common inference drawn from such studies is that the sex of the offspring is determined by the Y chromosome.
The monocots are one of the two major groups of flowering plants, the other being the dicots. In order to reproduce they utilize various strategies such as employing forms of asexual reproduction, restricting which individuals they are sexually compatible with, or influencing how they are pollinated. Nearly all reproductive strategies that evolved in the dicots have independently evolved in monocots as well. Despite these similarities and their close relatedness, monocots and dicots have distinct traits in their reproductive biologies.
Sexual selection is described as natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Sexual selection is a common concept in animal evolution but, with plants, it is oftentimes overlooked because many plants are hermaphrodites. Flowering plants show many characteristics that are often sexually selected for. For example, flower symmetry, nectar production, floral structure, and inflorescences are just a few of the many secondary sex characteristics acted upon by sexual selection. Sexual dimorphisms and reproductive organs can also be affected by sexual selection in flowering plants.
Rumex hastatulus, commonly known as the heartwing sorrel, is an annual flowering plant species in the family Polygonaceae otherwise known as the buckwheat family. It is found spread out through the eastern and southern United States.
Gametophytic selection is the selection of one haploid pollen grain over another through the means of pollen competition, 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.
References
- 1 2 Stehlik, I.; Barrett, S. C. H. (2006). "Pollination Intensity Influences Sex Ratios in Dioecious Rumex Nivalis, A Wind-Pollinated Plant". Evolution. 60 (6): 1207–1214. doi: 10.1111/j.0014-3820.2006.tb01199.x . PMID 16892971.
- ↑ Smith, B. W. (1963). "The Mechanism of Sex Determination in Rumex Hastatulus". Genetics. 48 (10): 1265–1288. doi:10.1093/genetics/48.10.1265. PMC 1210418 . PMID 17248184.
- ↑ Taylor, D. R. (1999). "Genetics of Sex Ratio Variation among Natural Populations of a Dioecious Plant". Evolution. 53 (1): 55–62. doi:10.2307/2640919. JSTOR 2640919. PMID 28565174.