Direction or Identification of Haploids Morphology,Genetic Markers,Coleoptile Thickness,Cytological Confirmation

Scholarships Dictionary Visa Details Study Abroad Exam Results Online Test Jobs

	Home
Production and Uses of Haploids Production and Uses of Haploids Introduction Production of Haploids Anther and Microspore Culture Ovule Culture Chromosome Elimination Somatic Reduction and Chromosome Elimination Mechanism of Chromosome Elimination Detection or Identification of Haploids Use of Haploids in Plant Breeding Programmes Use of Haploids in Species with Disomic Inheritance Hybrid Sorting in Haploid Breeding Some high Yielding Crop Varieties through Hybrid Sorting Using Anther Culture

Home >> Plant Biotechnology and Genomics >> Production and Uses of Haploids >>Decttion or Identification of Haploids

	Detection or Identification of Haploids A number of methods have been developed for the detection of haploids in a population of diploids. Although the most effective method is the use of genetic markers to be discussed in the next section, phenotypic effects can also be used for identification of haploids. The size of vegetative and floral parts and also that of the cells in haploids are reduced relative to diploids. In maize some success was achieved in the identification of haploids on the basis of coleoptile thickness. Stomata size, pollen size and pollen abortion can be other criteria to help initial screening, although in each case cytological confirmation will be essential.
Genetic Markers Many genetic marker systems are used for recognizing the haploids. The basic principle involved is that the hybrids and nonhybrids should differ, so that any failure of fertilization and parthenogenetica development of embryo can be recognized in the progeny at the seed stage, seedling stage or adult plant stage. For instance, if a female parent in a cross carries a recessive marker and is pollinated by dominant stock, then any recessive progeny would be generally a maternal haploid, although possibility also exists of its being a diploid of one of the following types (i) diploid hybrids, with mutation or deficiency for the marker gene in male parent, (ii) diploid hybrids with suppression of dominant marker, due to a suppressor gene or due to a disease (iii) diploids which are maternal due to apomictic development.
If the identification of haploids needs to be done at the seed stage, then the marker should express itself in the late stage of embryo development, such as aleurone colour marker. If screening is to be done at seedling stage, then the marker has been extensively used in developing maize monoploids. Most extensively used markers included ‘a1’ for brown coloured aleurone, plant and root and Ig fro liguleless, their corresponding dominant markers being ‘A’ for purple colour and ‘Lg’ for liguled character. If the female parent carries ‘a’ and / or lg, then in crosses with male parent carrying ‘A’ and/or ‘Lg’, the monoploids will be recognized by lack of purple colour and/or ligule. Another critical marker gene is ‘R’ allele (Rnj – cudu), which produces deep pigmentation of aleurone, and thus allows screening at the dormant seed stage.
Other markers included purple plumule (A, Pu1, Pu2), scutellum colour (A, C, R genes, and S1, S2 and S3 genes), and purple coleorrhiza (Pc1, Pc2, Pc3 and Pc4). These markers did not prove to be equally useful, because the frequency of these markers in maize populations is otherwise also quite high. Endosperm markers, however, are not as useful because very often monoploid embryo in the seed is associated with triploid endosperm, so that the latter will exhibit the male dominant endosperm trait. It should also be noted that for the recognition of paternal or androgenetic haploids, the dominant marker should be present in the female present so that the androgenetic haploids may be phenotypically different form the hybrid.
	In most of the above cases when genetic markers are used, 90-98% of the progeny can be discarded rather early and a very high frequency of haploids are recovered in the remaining population. The above technique of using genetic markers is particularly useful for the development of inbred lines in maize, but in crops like barley and wheat which are self pollinated and where doubled haploids need to be used for cultivation, the availability and utility of genetic markers may be limited.

	Home
Comparison of Pedigree and Bulk Methods of Conventional Plant Breeding Production of Spontaneously Doubled Haploids for Breeding Use of Haploids in Species with Polysomic Inheritance Analytical Breeding in Potato Two Breeding Schemes Using 2n Gametes in Potato Analytical Synthetic Breeding for Potato Limitations to Haploid Breeding Other Uses of Haploids Mutation Research Gametoclonal Variation Cytogenetics Research Evolutionary Studies Genetic Studies

Language >> English | Français | Español | Deutsch | Italiano | Portugues | Japanese | Korean | Sim-Chinese