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

References in periodicals archive ?
In this review we have dealt with three routes to haploidy, alternative to natural, zygotic embryogenesis and male gamete development in angiosperms (Fig.
The problem of haploidy (Cytogenetic studies in Nicotiana haploids and their bearing on some other cytogenetic problems).
Given the close evolutionary relationship between the two groups, the ancestral state in the progenitor of the apicomplexans and dinoflagellates was probably haploidy.
This evidence for recombination, taken together with our finding of haploidy, lends strong support to Symbiodinium life cycle (a), as proposed by Fitt and Trench (1983).
Neither haploidy nor any life cycle that retains both phases is ever stable here.
Equation (8) reveals that one and only one life cycle (either haploidy or diploidy, depending on the parameters) will be stable to invasion by modifiers of small effect.
For these biologically reasonable values, the strength of selection favoring an allele that changes the life cycle from complete haploidy to complete diploidy is 0.
Haploidy is favored either with complete linkage or when mutations are highly deleterious or partially dominant.
Reverting to haploidy exposes mutations that have previously been masked in diploids, making the spread of haploidy difficult.
Chapter 11 deals with self-incompatibility and pollen rejection in angiosperms, although it has little relevance in a book on haploidy.
Chapter 18 summarizes how the haploidy approach has helped the crop improvement programs and discusses the agronomic performance of anther culture-derived cultivars, some with wide adaptation or disease resistance, released for general cultivation.
Chapters 11, 16, and 17, have little relevance in a volume dealing with haploidy.