DIFFERENCE IN BACK CROSS AND TEST CROSS
- 1. PRESENTED BY- Leenakshi Tyagi & Karishma Khanna M.Sc Botany
- 2. Gregor Mendel established two types of crosses: the test cross and the backcross. In a test cross, a dominant phenotype is crossed with the homologous recessive genotype to distinguish between homologous dominant and heterozygous genotypes. Backcrossing involves crossing the F1 with either one of the parents or a genetically similar person to the parent. The primary distinction between a test cross and a backcross is that a test cross is used to determine the genotype of a phenotypically dominant individual, whereas a backcross is used to recover a dominant genotype from a parent who has an extreme genotype.
- 3. The breeding of F1 hybrid with one of the two parents is referred to as a backcross. When F1 crosses with the homozygous dominant, the progeny have a 100% dominant trait. When an F1 is mated with a recessive phenotype, the offspring have 50% dominant and 50% recessive traits. This hybrid generates offspring that are genetically identical or closely related to the F1's parents. As a result, backcrossing is widely utilized in horticulture and animal breeding to produce genetically identical offspring harboring elite genes.
- 4. Back cross with homozygous dominant parent Back cross with homozygous recessive parent
- 5. The hybrids that are backcrossed are known as 'BC' hybrids. For example, a BC1 hybrid is an F1 hybrid that was crossed with one of its parents or a genetically similar species. The BC2 hybrid is defined as a BC1 hybrid that has been crossed with the same parent or genetically similar species. Other instances include backcrossing in animals. A system of breeding in which repeated backcrosses are made to transfer a specific character to a well-adapted variety for which the variety is deficient is referred to as backcross breeding This approach is infrequently utilized in vegetatively propagated crops such as sugarcane and potatoes, and only with slight alterations.
- 6. APPLICATION- The backcross approach is commonly used to increase certain characteristics of a well-adapted variety that are lacking, like as resistance to a particular disease. The Backcross method is applicable in all three groups of crop plants, viz. self- pollinated, cross-pollinated, and asexually propagated. PARENTAL MATERIAL- The backcross procedure includes two types of parents: recipient parents and donor parents. - The parent who obtains a desired character is known as the receiving parent. The recipient parent is regularly employed in the backcross procedure, hence it is also known as the recurrent parent. The recipient parent is often a well-adapted, high- yielding variety from a region that is lacking in one or a few characteristics. - The parent that contributes the desirable character is known as the donor parent. Because the donor parent is only utilized once in the crossing, it is sometimes referred to as a nonrecurrent parent. The donor parent has low agronomic characteristics.
- 7. GENETIC CONSTITUTION- The backcross approach preserves the genotype of the original variety except for the attribute that is enhanced by backcrossing. In other words, the new variety resembles the parent variety in all the characters save the character being transferred. NUMBER OF BACK CROSS- Generally, 5 to 6 backcrosses are adequate to keep the genotype of the original variety while adding new characteristics. ACHIEVEMENTS IN BACK CROSS- -It has also been utilized for interspecific gene transfer and the creation of multiline variations in self-pollinated species. This strategy has resulted in the development of multiple disease-resistant varieties of wheat, cotton, and other crops. -Cotton variants V797, Digvijay, Vijalpa, and Kalyan, all of which belong to the Gossypium herbaceum family, were produced by backcrossing.
- 8. A test cross is a genetic technique for determining an unknown genotype in a dominant person. It is a breeding procedure in which a (known genotype) homozygous recessive individual is paired with an individual of the opposite mating type who has an unknown dominant genotype. The phenotypic characteristics of the resulting children are investigated, and the genotype of the examined individual is determined appropriately. If all of the progeny from the test cross are dominant, we may conclude that the genotype of the tested unknown person is homozygous dominant. If 50% of kids exhibit dominant traits and the remaining 50% exhibit recessive traits, we may conclude that the genotype of the tested unknown individual is heterozygous dominant.
- 9. A single gene test cross' is a test cross in which just one kind of gene or phenotypic trait is investigated. Only one of the test persons' dominant characteristics is taken into consideration. In a monohybrid test cross, if the test individual is heterozygous, the phenotypic ratio is 1:1.
- 10. A 'two-gene test cross' is a test cross that investigates two types of genes or phenotypic characteristics. Only two of the test subjects' dominant characteristics are examined. A test individual with two selected dominant phenotypic features is bred with double recessive parents, and the phenotypic characteristics of the F1 generations are investigated. In a dihybrid test cross, if the test individual is heterozygous, the phenotypic ratio is 1:1:1:1.
- 11. A 'triple gene test cross' is a form of testcross that examines three different types of genes or phenotypic characteristics. Only three dominating characteristics of test persons are evaluated. A test individual with three selected dominant phenotypic features is bred with a triple recessive parent, and the phenotypic characteristics of the F1 generations are investigated. If the test individual is heterozygous, the trihybrid test cross yields a phenotypic ratio of 1:1:1:1:1:1:1.
- 13. To determine the genotype of a dominant individual (F1 generation and a dominant parent). To determine the types and quantity of gametes produced. Separate pure and hybrid dominant breeds. LIMITATIONS OF TEST CROSS To identify the genotype of a dominant individual (F1 generation and dominant parent). Determine the kind and number of gametes generated. Separate pure and hybrid dominant breeds.