Transgressive variation refers to the occurrence of individuals within a population who exhibit traits or characteristics that differ significantly from the norm or average within that population. These variations can be physical, behavioral, or both, and can occur as a result of genetic mutations, environmental influences, or a combination of both.
Transgressive variation is an important concept in biology, as it allows for the potential for evolutionary change and adaptation within a population. In some cases, these variations may provide an advantage to the individual in terms of survival and reproduction, leading to their inclusion in the gene pool of future generations. In other cases, transgressive variations may be disadvantageous or even detrimental to the individual's survival, leading to their eventual elimination from the population.
One example of transgressive variation can be seen in the field of plant breeding, where plant breeders intentionally create new plant varieties by crossing individuals with desired traits in order to create offspring with a combination of those traits. This process can result in the creation of new plant varieties that exhibit traits that are significantly different from their parent plants.
Transgressive variation can also occur naturally within populations, as a result of genetic mutations or environmental influences. For example, some animals may exhibit unusual coloration or physical characteristics due to genetic mutations that occur during development. These variations may provide an advantage to the individual in terms of survival and reproduction, leading to their inclusion in the gene pool of future generations.
Transgressive variation is also an important concept in the field of psychology, where it can be used to explain individual differences in behavior and cognition. For example, some individuals may exhibit unusual or exceptional abilities in certain areas, such as mathematics or music, due to genetic or environmental influences that have resulted in transgressive variation.
In conclusion, transgressive variation refers to the occurrence of individuals within a population who exhibit traits or characteristics that differ significantly from the norm or average within that population. These variations can be beneficial or detrimental to the individual's survival and reproduction, and can occur as a result of genetic mutations or environmental influences. Understanding transgressive variation is important in a variety of fields, including biology, psychology, and plant breeding, as it helps to explain individual differences and the potential for evolutionary change within a population.
Transgressive Variation for Yield Components Measured throughout the Growth Cycle of Jefferson Rice (Oryza sativa) Ă— O. rufipogon Introgression Lines
Sexual recombination and asexual reproduction have expanded and diversified grape germplasm collections This et al. Breeders typically cross two pure line parents that are genetically diverse, complement for key defensive traits, and have proven yield potential within the target population of environments TPE that are typical for commercial production within a defined geographic zone. Crossing genetically diverse lines provides the breeder with a larger array of genetic variation in the offspring from which to make selections, enhancing the possibility of identifying offspring that outperform the "better parent" by a substantial amount. In addition, identification and introgression of QTLs from different AA genome wild species, including from O. In some instances the characters of F 2 exceed the parameters of the P, generation, which is normally maintained in the F In other words — suppose the parents differ in length between 2 — 6 cm, any spectrum exhibited by F 2 must be within this parameter. Host-plant resistance is highly effective in controlling crop loss from root-knot nematode RKN M. Based on the map positions, it can be postulated that HD QTL on 5A may be similar to the VRN1 gene mapped on chromosome 5A in T.
The wild allele for the QTL on 5A will increase the value of HD and so is responsible for the late flowering of T. Abdul Mujeeb-Kazi, in Emerging Technologies and Management of Crop Stress Tolerance, Volume 2, 2014 9. Further, if resources are not the limitation, tests for PAs may be extended to segregate generations in yield trials, depending on when genetic gains from selection are optimal Reynolds et al. The use of molecular markers can greatly improve the efficiency of the process, and markers are often used in combination with backcrossing to capture positive transgressive variation for rice improvement. Typically, the first two years are used to produce a vast array of unique F3 to F5-derived RILs that are subsequently screened for up to five more years for yield potential and other desirable agronomic traits. Breeding for optimal resistance must be based on selection of progeny with combinations of genes homozygous for resistance.
The two loci were located at the chromosomes 2H and 7H, and could explain 12. Drought escape, for example, under water-limited conditions via manipulation of plant phenology is a commonly used genetic approach for relative yield stability Richards, 1991. Since the number of recombination events in these cases is relatively small, genes or quantitative traits are mapped to large chromosomal blocks, and the resolution is low Mb scale. Since the advent of the first DNA markers, marker-assisted selection MAS has been viewed as a promising approach to streamline resistance breeding. However, much more remains to be learned on this topic before plant breeders can claim de novo variation as a cornerstone of their breeding programs. Breeding approaches based on specific PAs are useful only if defined appropriately in terms of the developmental stage of the plant, the specific attributes of the target environment for which they are adaptive, and their potential role in yield Reynolds and Trethowan, 2007; Mujeeb-Kazi et al. Phenotypes that result from epistatic interactions among genes differ from what would be expected if the loci were acting independently.
Difference between “Transgressive Variations” and “Regressive Variations”
In the case of WU, measurements related to stomatal conductance, such as canopy temperature CT , offer indirect indicators of uptake by roots Reynolds and Tuberosa, 2008. However, because of the crude traditional oil-milling process, defatted meal or oilcakes are largely only used today in animal feed mixtures or in fertilizers. Novel sources and enhanced levels of pathogen resistance are desirable for genetic improvement of crop plants. These workers found allelic reductions in every part of the wheat genome, with significant reduction beginning in the 1930s. Detection of such drought-adaptive PAs and the mechanisms involved is laborious, costly, and time consuming; however, the benefits are likely to be significant if successful. In high concentrations, in nonruminants like swine and poultry, it hydrolyzes to form thiocynates, isothiocynates, or nitriles and can adversely affect iodine uptake by the thyroid gland and can result in weight loss Fenwick et al.
Eizenga and Jeremy D. Because meiotic recombination shuffles genetic material between chromosomes and causes LD to decay with distance, markers that show high LD with a trait are likely to be physically linked to the functional mutation. Therefore, the most important breeding objective in Brassica breeding has been genetic modification of seed quality by changing the proportion of fatty acids suitable for nutritional and industrial purposes. Perhaps the most unusual result of this experiment is the fact that genetic variation remains even after more than 100 generations of selection in a closed population. The method is especially useful for characters with simple genetic patterns. Secondly, it is necessary to allow for epistatic and population specific effects i. One cause can be due to recombination of additive alleles.
Transgressive segregation has also been observed for Verticillium wilt resistance in an F 2 resistant Pima S-7Ă—susceptible Acala 44 Bolek et al. Environmental Other than the genetic factors solely causing transgressive segregation, environmental factors can cause genetic factors to take place. SSRs represent a rapidly evolving highly mutable fraction of eukaryotic genomes. So, any technique that can minimize these selection errors can dramatically improve the efficiency of the breeding program and the true performance advantage of new products. The origins of the experiment were influenced primarily by work conducted in France by early breeders of the fodder beet Hopkins, 1899; Troyer, 1996; Dudley and Lambert, 1992 , and the early focus of this experiment was modification of the corn kernel's chemical makeup. If the population has a long history of inbreeding, LD will decay slowly and the resolution of the association mapping study will be quite low.
The experiment was conceived by Cyril Hopkins, a chemist. A common refrain about modern plant breeding is the concern about its potential to reduce genetic diversity by increasing selection pressure on the uniform conditions typical of modern agriculture. Also, because partial-selfing in rice can lead to spurious inferences of population structure, it is necessary to modify existing methodologies to jointly infer population structure and population-specific selfing rates. GBM1251 chromosome 2H and GBR441 chromosome 4H were the markers most closely associated with these QTLs. The biparental cross between inbred parent lines is a common starting point for generating recombinant inbred line RIL populations that can be screened for improved inbred cultivars.
The enhanced Al tolerance may be due to transgressive segregation, suggesting that more than one locus could exist in determining Al tolerance. Transgressive segregants have also been identified in Auburn 623 RNR and some N lines. Edwards , +2 authors A. Molecular markers are now routinely used in plant cultivar development to assist backcrossing of major genes into elite cultivars and to select alleles with major effects on high-value traits with relatively simple inheritance. Major QTLs for resistance of nematode disease have been identified in Acala NemXĂ—Acala SJ-2, Acala SJ-2Ă—Clevewilt, and Pima S-7Ă—Acala NemX Wang et al. The high-performance quantitative GLC technique McGregor et al. This generally results from cooperation or interaction between the genes present in the two parental types.
