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History[ edit ] The first report of the haploid plant was published by Blakeslee et al. Subsequently, haploids were reported in many other species. Guha and Maheshwari developed an anther culture technique for the production of haploids in the laboratory. Haploid production by wide crossing was reported in barley Kasha and Kao, and tobacco Burk et al.
Tobacco, rapeseedand barley are the most responsive species for doubled haploid production. Doubled haploid methodologies have now been applied to over species. Haploid embryos are produced in vivo by parthenogenesispseudogamyor chromosome elimination after wide crossing.
The haploid embryo is rescued, cultured, and chromosome-doubling produces doubled haploids. The in vitro methods include gynogenesis ovary and flower culture and androgenesis anther and microspore culture. Another method of producing the haploids Impetus of the dhs wide crossing. In barley, haploids can be produced by wide crossing with the related species Hordeum bulbosum; fertilization is affected, but during the early stages of seed development the H.
In tobacco Nicotiana tabacumwide crossing with Nicotiana africana is widely used. Although these percentages appear small, the vast yield of tiny seeds and the early death of most seedlings provide significant numbers of viable hybrids and haploids in relatively small soil containers.
This method of interspecific pollination serves as a practical way of producing seed-derived haploids of N. Thus, if AA is desirable genotype, the probability of obtaining this genotype is higher in haploid method than in diploid method.
Hence the efficiency of the haploid method is high when the number of genes concerned is large. Studies were conducted comparing DH method and other conventional breeding methods and it was concluded that adoption of doubled haploidy does not lead to any bias of genotypes in populations, and random DHs were even found to be compatible to selected line produced by conventional pedigree method.
Although the potential of DH populations in quantitative genetics has been understood for some time, it was the advent of molecular marker maps that provided the impetus for their use in identifying loci controlling quantitative traits. As the quantitative trait loci QTL effects are small and highly influenced by environmental factors, accurate phenotyping with replicated trials is needed.
This is possible with doubled haploidy organisms because of their true breeding nature and because they can conveniently be produced in large numbers. Using DH populations, quantitative traits have been mapped in nine crop species. A problem in this procedure is being able to identify the lines carrying the trait of interest at each generation.
The problem is particularly acute if the trait of interest is recessive, as it will be present only in a heterozygous condition after each backcross. The development of molecular markers provides an easier method of selection based on the genotype marker rather than the phenotype.
Combined with doubled haploidy it becomes more effective. In marker assisted backcross conversion, a recipient parent is crossed with a donor line and the hybrid F1 backcrossed to the recipient. The resulting generation BC1 is backcrossed and the process repeated until the desired genotypes are produced.
The combination of doubled haploidy and molecular marker provides the short cut. In the back cross generation one itself a genotype with the character of interest can be selected and converted into homozygous doubled haploid genotype.
Bulked segregant analysis BSA [ edit ] In bulked segregant analysisa population is screened for a trait of interest and the genotypes at the two extreme ends form two bulks.
Then the two bulks are tested for the presence or absence of molecular markers. Since the bulks are supposed to contrast in the alleles that contribute positive and negative effects, any marker polymorphism between the two bulks indicates the linkage between the marker and trait of interest.
BSA is dependent on accurate phenotyping and the DH population has particular advantage in that they are true breeding and can be tested repeatedly.
DH populations are commonly used in bulked segregant analysis, which is a popular method in marker assisted breeding. Genetic maps[ edit ] Genetic maps are very important to understand the structure and organization of genomes from which evolution patterns and syntenic relationships between species can be deduced.
DH populations have become standard resources in genetic mapping for species in which DHs are readily available. Doubled haploid populations are ideal for genetic mapping. It is possible to produce a genetic map within two years of the initial cross regardless of the species.
Map construction is relatively easy using a DH population derived from a hybrid of two homozygous parents as the expected segregation ratio is simple, i. DH populations have now been used to produce genetic maps of barley, rapeseed, rice, wheat, and pepper.
DH populations played a major role in facilitating the generation of the molecular marker maps in eight crop species. A small doubled haploid DH population was used to demonstrate that a dwarfing gene in barley is located chromosome 5H.The core of the system consists of two MW Solar Taurus 60S dual-fuel gas turbines.
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