Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, to achieve offspring with a genetic identity closer to that of the parent. It is used in horticulture, animal breeding, and production of gene knockout organisms.
Backcrossed hybrids are sometimes described with acronym "BC"; for example, an F1 hybrid crossed with one of its parents (or a genetically similar individual) can be termed a BC1 hybrid, and a further cross of the BC1 hybrid to the same parent (or a genetically similar individual) produces a BC2 hybrid.[1]
In practice, sections of genome from the nonrecurrent parents are often still present and can have unwanted traits associated with them.
For very wide crosses, limited recombination may maintain thousands of "alien" genes within the elite cultivar.
Many backcrosses are required to produce a new cultivar, which can take many years.
Natural backcrossingsedit
York radiate groundsel (Senecio eboracensis) is a naturally occurring hybrid species of Oxford ragwort (Senecio squalidus) and common groundsel (Senecio vulgaris). It is thought to have arisen from a backcrossing of the F1 hybrid with S. vulgaris.[2]
Again, the pure tall (TT) and pure dwarf (tt) pea plants when crossed in the parental generation, produce all heterozygote (Tt) tall pea plants in the first filial generation. The cross between first filial heterozygote tall (Tt) pea plant and pure tall (TT) or pure dwarf (tt) pea plant of the parental generation is also an example for the back-crossing between two plants. In this case, the filial generation formed after the back cross may have a phenotype ratio of 1:1 if the cross is made with recessive parent or else all offspring may be having phenotype of dominant trait if the backcross is with a parent having the dominant trait. The former of these traits is also called a test cross.
This image demonstrates backcrossing of a heterozygous mouse from one genetic background onto another genetic background. In this example, the gene knockout is performed on 129/Sv cells and then backcrossed into the C57B/6J genetic background. With each successive backcross, the percentage of C57B/6J DNA that constitutes the genome of the offspring is increased.
Backcrossing may be deliberately employed in animals to transfer a desirable trait in an animal of inferior genetic background to an animal of preferable genetic background. In gene-knockout experiments in particular, where the knockout is performed on easily culturedstem cell lines, but is required in an animal with a different genetic background, the knockout animal is backcrossed against the animal of the required genetic background. As the figure shows, each time that the mouse with the desired trait (in this case the lack of a gene (i.e. a knockout), indicated by the presence of a positive selectable marker) is crossed with a mouse of a constant genetic background, the average percentage of the genetic material of the offspring that is derived from that constant background increases. The result, after sufficient reiterations, is an animal with the desired trait in the desired genetic background, with the percentage of genetic material from the original stem cells reduced to a minimum (on the order of 0.01%).[3]
Due to the nature of meiosis, in which chromosomes derived from each parent are randomly shuffled and assigned to each nascent gamete, the percentage of genetic material deriving from either cell line varies between offspring of a single crossing, but will have an expected value. The genotype of each member of offspring may be assessed to choose not only an individual that carries the desired genetic trait, but also the minimum percentage of genetic material from the original stem cell line.[4]
A consomic strain is an inbred strain with one of its chromosomes replaced by the homologous chromosome of another inbred strain via a series of marker-assisted backcrosses.[5]
^Schweitzer, J.A.; Martinsen, G.D.; Whitham, T.G. (2002). "Cottonwood hybrids gain fitness traits of both parents: a mechanism for their long-term persistence?". American Journal of Botany. 89 (6): 981–990. doi:10.3732/ajb.89.6.981. PMID 21665697.
^Abbot, R.J.; Lowe, A.J. (2003). (PDF). Watsonia. 24: 375–388. Archived from the original (PDF) on 2007-09-27. Retrieved 2007-07-15.
^. Archived from the original on 2006-09-09. Retrieved 2008-01-01.
^Frisch M, Melchinger AE (2005). "Selection theory for marker-assisted backcrossing". Genetics. 170 (2): 909–17. doi:10.1534/genetics.104.035451. PMC1450430. PMID 15802512.
^The Jackson Laboratory > Consomic strains 2011-06-24 at the Wayback Machine Last Modified: June 11, 2010
External linksedit
- education and training materials for plant breeders and allied professionals
February 16, 2024
backcrossing, confused, with, breeding, back, crossing, hybrid, with, parents, individual, genetically, similar, parent, achieve, offspring, with, genetic, identity, closer, that, parent, used, horticulture, animal, breeding, production, gene, knockout, organi. Not to be confused with Breeding back Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent to achieve offspring with a genetic identity closer to that of the parent It is used in horticulture animal breeding and production of gene knockout organisms Backcrossed hybrids are sometimes described with acronym BC for example an F1 hybrid crossed with one of its parents or a genetically similar individual can be termed a BC1 hybrid and a further cross of the BC1 hybrid to the same parent or a genetically similar individual produces a BC2 hybrid 1 Contents 1 Plants 1 1 Advantages 1 2 Disadvantages 1 3 Natural backcrossings 1 4 Artificially recombinant lines 2 Animals 3 See also 4 References 5 External linksPlants editAdvantages edit If the recurrent parent is an elite genotype at the end of the backcrossing programme an elite genotype is recovered As no new recombination results the elite combination is not lost Disadvantages edit It works poorly for quantitative traits It is more restricted for recessive traits In practice sections of genome from the nonrecurrent parents are often still present and can have unwanted traits associated with them For very wide crosses limited recombination may maintain thousands of alien genes within the elite cultivar Many backcrosses are required to produce a new cultivar which can take many years Natural backcrossings edit York radiate groundsel Senecio eboracensis is a naturally occurring hybrid species of Oxford ragwort Senecio squalidus and common groundsel Senecio vulgaris It is thought to have arisen from a backcrossing of the F1 hybrid with S vulgaris 2 Again the pure tall TT and pure dwarf tt pea plants when crossed in the parental generation produce all heterozygote Tt tall pea plants in the first filial generation The cross between first filial heterozygote tall Tt pea plant and pure tall TT or pure dwarf tt pea plant of the parental generation is also an example for the back crossing between two plants In this case the filial generation formed after the back cross may have a phenotype ratio of 1 1 if the cross is made with recessive parent or else all offspring may be having phenotype of dominant trait if the backcross is with a parent having the dominant trait The former of these traits is also called a test cross Artificially recombinant lines edit In plants the term inbred backcross line IBL refers to a line i e population of plants derived from the repeated backcrossing of a line with artificially recombinant DNA with the wild type operating some kind of selection that can be phenotypical or through a molecular marker for the production of an introgression line Animals edit nbsp This image demonstrates backcrossing of a heterozygous mouse from one genetic background onto another genetic background In this example the gene knockout is performed on 129 Sv cells and then backcrossed into the C57B 6J genetic background With each successive backcross the percentage of C57B 6J DNA that constitutes the genome of the offspring is increased Backcrossing may be deliberately employed in animals to transfer a desirable trait in an animal of inferior genetic background to an animal of preferable genetic background In gene knockout experiments in particular where the knockout is performed on easily cultured stem cell lines but is required in an animal with a different genetic background the knockout animal is backcrossed against the animal of the required genetic background As the figure shows each time that the mouse with the desired trait in this case the lack of a gene i e a knockout indicated by the presence of a positive selectable marker is crossed with a mouse of a constant genetic background the average percentage of the genetic material of the offspring that is derived from that constant background increases The result after sufficient reiterations is an animal with the desired trait in the desired genetic background with the percentage of genetic material from the original stem cells reduced to a minimum on the order of 0 01 3 Due to the nature of meiosis in which chromosomes derived from each parent are randomly shuffled and assigned to each nascent gamete the percentage of genetic material deriving from either cell line varies between offspring of a single crossing but will have an expected value The genotype of each member of offspring may be assessed to choose not only an individual that carries the desired genetic trait but also the minimum percentage of genetic material from the original stem cell line 4 A consomic strain is an inbred strain with one of its chromosomes replaced by the homologous chromosome of another inbred strain via a series of marker assisted backcrosses 5 See also editIntrogression IncestReferences edit Schweitzer J A Martinsen G D Whitham T G 2002 Cottonwood hybrids gain fitness traits of both parents a mechanism for their long term persistence American Journal of Botany 89 6 981 990 doi 10 3732 ajb 89 6 981 PMID 21665697 Abbot R J Lowe A J 2003 A new British species Senecio eboracensis Asteraceae another hybrid derivative of S vulgaris L and S squalidae L PDF Watsonia 24 375 388 Archived from the original PDF on 2007 09 27 Retrieved 2007 07 15 Embryonic Stem Cell Archived from the original on 2006 09 09 Retrieved 2008 01 01 Frisch M Melchinger AE 2005 Selection theory for marker assisted backcrossing Genetics 170 2 909 17 doi 10 1534 genetics 104 035451 PMC 1450430 PMID 15802512 The Jackson Laboratory gt Consomic strains Archived 2011 06 24 at the Wayback Machine Last Modified June 11 2010External links editThe Plant Breeding and Genomics Community of Practice on eXtension education and training materials for plant breeders and allied professionals Retrieved from https en wikipedia org w index php title Backcrossing amp oldid 1193313236, wikipedia, wiki, book, books, library,
