Haploidy


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Related to Haploidy: diploidy, haploids

Haploidy

 

the opposite of polyploidy; a phenomenon that involves the multiple reduction of the number of chromosomes in the offspring in comparison to the maternal individual. Haploidy, as a rule, is the result of the development of the embryo from reduced (haploid) gametes or from cells that are functionally equivalent to gametes by means of apomixis—that is, without fertilization. Haploidy is rarely encountered in the animal world but is common among flowering plants. It has been recorded in more than 150 species of plants from 70 genera of 33 families (including plants from the families Gramineae, Solanaceae, Orchidaceae, and legumes). The phenomenon occurs in all major cultivated plants: wheat, rye, corn, rice, barley, sorghum, potatoes, tobacco, cotton, flax, beets, cabbage, pumpkins, cucumbers, and tomatoes. It also occurs in fodder grasses, including meadow grass, bromegrass, timothy, alfalfa, and vetch.

Haploidy is genetically determined and is encountered in certain species and varieties with a predictable frequency. (For example, in corn there is one haploid per 1,000 diploid plants.) In the evolution of species, haploidy provided a unique mechanism for reducing the level of ploidy. Haploidy is used in the solution of many genetic problems, including determination of the effect of a dose of a gene, obtaining aneuploids, the study of the genetics of quantitative traits, and the analysis of genomes. In the selection of plants equivalent, self-fertilized strains are obtained from the haploids by doubling the number of chromosomes of the homozygous strain. These plants are used to produce hybrid seeds (for example, in corn) as well as to transpose the selection process from the polyploid to the diploid level (for example, in potatoes). The special type of haploidy known as androgenesis, in which the sperm nucleus replaces the nucleus of the ovum, is used to obtain sterile male analogues in corn.

REFERENCES

Kirillova, G. A. “Iavlenie gaploidii u pokrytosemennykh rastenii.” Genetika, 1966, no. 2.
Gaploidiia u pokrytosemennikh rastenii, part 1. Saratov, 1970.
Kimber, G., and R. Riley. “Haploid Angiosperms.” Botanical Review, 1963, vol. 29, no. 4. Pages 480-531.
Magoon, M. L., and K. R. Khanna. “Haploids.” Caryologia, 1963, vol. 16, no. 1, pp. 191-255.

S. S. KHOKHLOV

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Given the economic impact of these species and/or their suitability for both fundamental and applied research, parallel efforts have been made to circumvent their extreme recalcitrancy by exploring alternative pathways to androgenic haploidy, whereas in species more easily inducible to microspore embryogenesis, focusing on alternatives is unnecessary in practice, and resources can be devoted to investigate more promising ways to doubled haploidy.
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