Androgenesis

androgenesis

[‚an·drə′jen·ə·səs]

(embryology)

Development of an embryo from a fertilized irradiated egg, involving only the male nucleus.

Androgenesis

 

development of an egg cell with a male nucleus that has been introduced by sperm in the process of fertilization.

Androgenesis is observed in certain species of animals (silkworms) and plants (tobacco, corn) in cases where the maternal nucleus is destroyed before fertilization, which in such cases is false; that is, the female and male nuclei are not united, and only the male nucleus participates in the segmentation. Androgenesis is a special case of virgin development, or parthenogenesis; it is sometimes called male parthenogenesis. It may be caused artificially when either the nucleus of the egg cell itself is removed (for example, by microsurgery, by centrifugation, or by snaking, all of which cause the nucleus-containing fragments to break off) or is damaged by specific nuclear poisons (“tripoflavin”), ionizing radiation, intense heat and other means, and finally degenerates. Experiments have been instituted to obtain an-drogenetic offspring from sharply differing parents (for example, with distant crossbreeding) for the purpose of solving the problem of which cell element—the cytoplasm obtained from the mother or the nucleus obtained from the father—controls the development of the inherited characteristics of the androgenetic individual. In almost all experiments, only the initial stages of the development of androgenetic zygotes were obtained. Such embryos are viable when the set of diploid chromosomes is restored, which is possible when the egg cell is simultaneously penetrated by several spermatozoa and a union of two paternal nuclei occurs. Cases in which only a part of the ovum’s cytoplasm participates in the development of an egg cell with a male nucleus are usually designated by the term “merogony.” Sexually mature animals (always males) have been obtained only in the case of the Chinese silkworm and the ichneumon fly Habrobracon juglandis. In regard to this, B. L. Astaurov and V. P. Ostriakova achieved (1956) complete interspecific androgenesis in animals for the first time by crossbreeding two species of silkworm. A few cases of complete androgenesis have been observed in plants, in cases of the distant crossbreeding of various species of tobacco, hawk’s-beard, and corn. In all cases of complete androgenesis the androgenetic offspring of both animals and plants have resembled the paternal species, which indicates the primacy of the cell nucleus in heredity. Thus it is possible by means of androgenesis to clarify a number of problems connected with nucleoplasmic relations and to evaluate the role of the cytoplasm and the nucleus in transmitting species characteristics. It is also used for the purpose of governing sex when it is necessary to obtain only male offspring (for example, in breeding silkworms).

REFERENCES

Astaurov, B. L. “Znachenie opytov po merogonii i androgenezu dlia teorii razvitiia i nasledstvennosti.” Uspekhi sovremennoi biologii, 1948, vol. 25, no. 1.
Astaurov, B. L., and V. P. Ostriakova-Varshaver. “Poluchenie polnogo geterospermnogo androgeneza u mezhvidovykh gibridov shelkovichnogo chervia.” Izv. AN SSSR: Ser. biologicheskaia, 1957, no. 2.

B. L. ASTAUROV