Significance Of Parthenogenesis

Parthenogenesis as a form of reproduction has established itself in a wide variety of organisms, both plants and animals. In certain respects parthenogenesis has advantages over sexual reproduction. Its significance lies in the following aspects.

1. Control of Sex Ratio. When the queen bee is fertilized by the drone, the spermatozoa are deposited in the seminal receptacles. A single mating is sufficient to fertilize the eggs for the lifetime of the queen.The queen controls fertilization in some manner not known, and thus controls the sex ratio. Fertilized eggs develop into diploid females (queen or workers) while unfertilized eggs develop parthenogenetically into haploid males (drones). In a hive there may be 20,000 to 80,000 workers(diploid sterile females). Drones which do no work, number in just tens or hundreds.

2. Rapid Breeding. In aphids (plant lice) female reproduce in summer by diploid parthenogenesis. Several generations of females are formed.The rapid increase in numbers is due to the fact that the entire population consists of breeding females. Also the delay  resulting from the time spent in finding a mate and mating is eliminated.

3. Relation To Hybridization. When a hybrid is formed between two species, the chromosomes are to some extent unmatched. This results in difficulties during maturation divisions of meiosis, because chromosome pairing becomes difficult. Normal reproduction by fertilization may become impossible in such cases. Diploid parthenogenesis is therefore the solution because no maturation divisions are undergone during the formation of the egg. New species arising as a result of hybridization have the combined haploid number of chromosomes of the two parents.

4. Relation To Polyploidy. When polyploids like triploids (3n) and pentaploids (5n) are formed, the odd number of chromosome sets makes normal meiosis difficult. This usually results in sterility.If parthenogenetic development is adopted it can bring about escape from sterility. Thus there is a co-relation between polyploidy and obligatory parthenogenesis. Polyploidy is more common in plants than in animals.

5.Variation. In total parthenogenesis, fertilization and meiosis are both eliminated. Thus there are no chances of genetic recombination. Since all the descendants have identical heredity there is practically no variation. Species having total parthenogenesis can thrive because they are well adapted to a particular environment. In these species  genetic variability has been sacrificed to preserve genotypes that have proved their value in survival.