Biological Sciences
Genetic Cross
A genetic cross is a breeding experiment performed to study the inheritance of traits in offspring. It involves mating individuals with different genetic makeups to observe how specific traits are passed on to the next generation. By analyzing the traits of the offspring, geneticists can gain insights into the patterns of inheritance and the underlying genetic mechanisms at play.
Written by Perlego with AI-assistance
Related key terms
1 of 5
5 Key excerpts on "Genetic Cross"
eBook - PDFGenetic Manipulation in Plant Breeding
Proceedings International Symposium Organized by EUCARPIA, September 8–13, 1985, Berlin (West), Germany
- W. Horn, C. J. Jensen, W. Odenbach, O. Schieder(Authors)
- 2019(Publication Date)
- De Gruyter(Publisher)
3 MUTATION BREEDING: A STEPPING-STONE BETWEEN GREGOR MENDEL AND GENETIC MANI-PULATION (A TREATISE FOR VEGETATIVELY PROPAGATED CROPS). A.M. van Harten Department of Plant Breeding (I.v.P.), Agricultural University, P.O. Box 386, 6700 AJ Uageningen, The Netherlands C. Broertjes Research Institute ITAL, P.O. Box 48, 6700 AA Wageningen, The Netherlands Introduction Plant breeders are permanently in need of new techniques that may help them in solving specific breeding problems. Therefore, scientific developments in related fields are followed closely and new approaches are tried out to test their applicability and to determine their potentialities and limitations. The ultimate objective of all breeding work is to produce in the most economic way improved cultivars that meet agricultural or horticultural needs. In practice this means that the breeder applies difficult and time-consuming selection procedures to genetically heterogeneous starting material that has either been collected or produced. Crossbreeding at the intraspecific level is the oldest and still by far the most important breeding method. However, in a growing number of cases, e.g. when resistances have to be introduced, this approach is not adequate anymore. More distant crosses may be needed and this leads to the introduction of many problems that are mainly related to all sorts of crossing-barreers that exist between species. Moreover, distant crosses usually result in the introduction of many unfavourable genes in addition to the desired ones. Repeated back-crossing is the solution, but this requires much time and labour. Especially in crops where a normal crossing program meets problems, breeders have always shown special interest in methods which lead to improving only one or very few unfavourable traits in an otherwise good and accepted cultivar. This situation occurs for instance in vegetatively propagated crops.
eBook - ePub- D. Phillip Sponenberg(Author)
- 2022(Publication Date)
- 5m Books Ltd(Publisher)
While several cautions have been raised against inbreeding and linebreeding, it is very important to remember that these are extremely useful breeding strategies in some situations and for some specific goals. The deleterious effects usually surface after several sequential generations of linebred or inbred matings. Over shorter periods they can each serve very positive roles in the management of gene pools. Inbreeding and linebreeding are power tools. They are effective when used appropriately, and dangerous when used carelessly.6.2 Outcrossing: Crossbreeding and Linecrossing
Outcrossing involves the mating of animals that are not related and is the philosophical and biological opposite of linebreeding. Outcrossing and outbreeding are synonyms, and the results are commonly characterized as outbred (as contrasted to inbred). Outcrossing can be divided into two subgroups: crossbreeding and linecrossing. Crossbreeding is the mating of animals from two different breeds. Linecrossing is the mating of unrelated animals from within the same breed. Usually these matings occur between animals from two different bloodlines within the breed, which leads to the term “linecrossing” (Figure 6.5 ).Figure 6.5Relative degrees of genetic relatedness resulting from different breeding strategies. Figure by DPS.Crossbreeding is a fascinating phenomenon, partly because different results occur depending upon which generation is considered. The first stage is the initial cross. A useful example comes from cattle. When Angus (black, polled) and Hereford (red, white-faced, horned) cattle are crossed, the initial result is a uniform crop of “black baldy” calves. The calves exhibit the dominant traits of both breeds: black and polled from Angus, and white face from Hereford. These offspring have benefitted from the specific combination of the genetic array of the parental breeds. This generation is called the F1 (first filial) generation. Each parental breed is uniform, each calf gets half of its genetic makeup from each parental breed. The result is great uniformity. This first calf crop is reaping the benefits of the two homogeneous parental breeds, as well as hybrid vigor that results from the two breeds being unrelated.
- Robert T. Gerlai(Author)
- 2018(Publication Date)
- Academic Press(Publisher)
n ) for a particular genome equals 1, the number of individuals tested from a given inbred strain can be as large as the experimenter wants.Breeding systems developed using inbred strains utilize such statistical methods, essentially modified variance analyses or bivariate, covariance-based, statistics.18 –21Examples of such breeding systems are the Mendelian cross17 ,18and the diallel cross19 ,20systems. The Mendelian cross system includes two inbred parental strains (P1 and P2 ), two reciprocal F1 generations (F1a = P1 female × P2 male; F1b = P1 male × P2 female), at minimum one F2 generation (F1 × F1 ), and two backcross generations (B1 = P1 × F1 ; B2 = P2 × F1 ). The diallel cross comprises of n number of inbred parental strains (with n =< 3) and the reciprocal F1 crosses between these parental strains in all possible combinations. Phenotypical characterization of the generations and strains of these breeding systems allows the investigator to reveal information on the pattern of inheritance, the genetic architecture. Genetic architecture in this case means how genes interact with each other and how they interact with the environment. For example, these breeding systems can be used to estimate the contribution of additive genetic effects and dominance-related effects (intralocus interactions) of alleles, as well as epistatic (interlocus) interactions among alleles to genetic variance. They also allow the dissection of phenotypical variance to environmental and genetic variance components. The bivariate extension of the diallel method even enables scientists to estimate correlations between traits solely arising from genetic effects or solely due to environmental effects.30
eBook - PDFConcise Encyclopedia of Crop Improvement
Institutions, Persons, Theories, Methods, and Histories
- Rolf Schlegel(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
One is the extraction and recombination of inbreds combined with selection to produce heterozygous but homogeneous hybrids, whereby combina-tions are first disturbed to complete the final order. The other is back-cross breeding, in which individual genes can be extracted and inserted with precision and predictability into new genetic back-grounds. The combination of backcross breeding to improve inbreds and hybrid breeding to capture heterosis is the basis of present day maize and other hybrid crop improvement (see Chapter 3.4). The success of the new science of plant breeding had a substantial impact on agriculture, horticulture, and forestry. Dramatic successes quickly followed; examples include hybrids and disease resistant crops. A further spectacular example of plant-breeding progress was 60 CONCISE ENCYCLOPEDIA OF CROP IMPROVEMENT the development of short-stemmed photoperiod-insensitive wheat and rice, the forerunners of the so-called “Green Revolution,” for which >>> N. BORLAUG, a plant breeder with the Center for the Improvement of Maize and Wheat, Mexico (CIMMYT) was to receive the Nobel Prize for Peace in 1970. 3.1. REDISCOVERY OF MENDEL’S LAWS—BEGINNING OF GENETIC RESEARCH H. de VRIES was always involved and fascinated about questions of the theory of the origin of species and the role mutation played in the evolution of plants. In addition, he carried out crossing experi-ments with Oenothera lamarckiana × O. brevistylis in 1895, where he observed the uniformity of his crossing hybrids and the “domi-nance” of some prevailing characters. The detection of a citation of MENDEL’s work in the book of FOCKE (1881) and the study of MENDEL’s publication guided VRIES to work with peas. In his first report about the segregation of his pea hybrids, he did not mention MENDEL’s name but used the expressions “dominant” and “reces-sive.” In the second, a more precise paper, he confirmed MENDEL’s result but concentrated again on his mutation theory.
eBook - PDF- Tomar, Arun Kumar(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Cannot be resold/distributed. of genes. The process which forms the recombinant gametes and produces the intermediate results is the crossing over . 5.2 CROSSING OVER Morgan postulated that recombination of linked genes is accompanied through a process by which the homologous chromosomes exchange parts (Johanssen, 1909). This process of physical exchange of parts between homologous chromosomes is called crossing over. The event of crossingover occurs between nonsister chromatids of homologous chromosomes at the time of synapsis during late prophase and metaphase of meiotic cell division. This involves actual exchange of chromosome material. Each of the four chromatids goes into separate gamete to form four gametes. The two gametes carry the gene combinations identical to the parents and other two gametes are produced by crossingover and hence called as crossover gametes or recombinants . These two recombinant gametes on fertilization produce two recombinant phenotypes which are different from parental phenotypes. These recombinant phenotypes are the result of crossing over. The percentage of recombinant is also referred to as the percentage of crossover which is simply the number of recombinant phenotypes expressed as a percentage of the total number of progeny. The cytological basis of the crossing over was described by Johanssen (1909) through the formation of chiasma at the tetrad stage during spermatogenesis in Salamonders. He noticed that during meiosis at the time of pairing ( Synapsis ) of duplicated homologous chromosomes (tetrads or four-strands), two sister chromatids showed a cross-shape structure with each other while the other two do not. This cross-shape structure of tetrads is called as Chiasma (plural- chiasmata). Thus chiasma is probably the visible manifestation of crossing over. Thus the crossing over occurs between chromatids and not between unduplicated chromosomes.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
