MonoploidyAn individual that contains one half the normal number of chromosomes is a monoploid and exhibits monoploidy. Monoploids are very rare in nature because recessive lethal mutations become unmasked, and thus they die before they are detected. These alleles normally are not a problem in diploids because their effects are masked by dominant alleles in the genome. Some species such as bees, ants and male bees are normally monoploid because they develop from unfertilized eggs. Consequently, these individuals will be sterile. A stage in the life cycle of some fungal species can also be monoploid.
Monoploidy has been applied in plant biotechnology to rapidly develop plants from anthers that have a fixed genotype. F1 plants derived from a cross of two parents are grown and anther tissue is used to regenerate new plants using tissue culture techniques. The plants that are derived from this tissue will be monoploid, and the genetics of these individuals can be studied or they can be treated with a chemical to double the chromosome number.
What are the advantages of this technique? Theoretically, different recombination products can be fixed much faster than with conventional plant breeding techniques. Plant breeders make crosses and begin selecting in the F2 generation for individuals that show desirable traits. But these selections are then tested in subsequent generations because the lines are not genetically homogeneous or homozygous. Several more generations of testing are normally required before the desired trait is fixed in a line.
Using anther culture, though, these recombinants in the F1 gametes are fixed immediately after the chromosomes are doubled (with a drug such as colchicine). They are fixed because after doubling the individual will be homozygous for every gene in the genome. Thus, selection for lines with desirable traits can be accelerated significantly. To date, the limiting factor has been the development of anther culture techniques for different crops. Wheat has been the best success story to date with this technique.
Copyright © 1997. Phillip McClean