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(cell and molecular biology)
One of the two nuclear bodies of a newly fertilized ovum, the male pronucleus and the female pronucleus, the fusion of which results in the formation of the germinal (cleavage) nucleus.



the haploid nucleus of a sex cell, or gamete. During fertilization, the diploid nucleus of the zygote, or synkaryon, is formed by the fusion of two pronuclei; the chromosome sets of both pronuclei are joined in the synkaryon.

In multicellular organisms and a number of protozoans that are anisogamous, there are female and male pronuclei. The female pronucleus is the nucleus of a mature egg cell, or macro-gamete. The male pronucleus is formed by the swelling of the nucleus of a spermatozoid, or microgamete, after it has become embedded in the cytoplasm of an egg cell. In isogamous unicellular organisms, the fusing pronuclei, like the gametes themselves, are morphologically indistinguishable. During autogamy, pronuclei that have been formed in the same cell fuse; they are usually sister nuclei. During conjugation in infusorians, two pronuclei form in each partner—a stationary pronucleus and a migrating pronucleus. There is first an exchange of migrating pronuclei between partners through a cytoplasmic bridge, which is followed by the fusion of the pronuclei in each of the partners.

References in periodicals archive ?
The male pronucleus condensed and remained quiescent until PB2 extrusion in the egg cytoplasm, at which point it began to swell.
With respect to the male pronucleus formation, activation of oocytes following ICSI could improve the development of male pronucleus formation in activated oocytes as compared to non-activated ones as such the difference has become significant in epididymal group.
In addition, the cytological studies revealed that the donor sperm incorporated into the egg cytoplasm, developed into the male pronucleus, and merged with the female pronucleus eventually in some interspecific crosses in molluscs, such as C.
After axonemal incorporation and nuclear translocation, the sperm chromatin decondenses and is encompassed by a membrane forming the male pronucleus.
First, a fertilizing sperm takes on a species-specific conformation inside embryos that may serve a role in positioning the male pronucleus before karyogamy (Karr 1991).