Pronucleus

: pronuclei) denotes the nucleus found in either a sperm or egg cell during the process of fertilization.

Two-pronuclear zygotes transitioning through 1PN or 3PN states tend to yield poorer-quality embryos compared to those maintaining 2PN status throughout development,[1] and this distinction may hold significance in the selection of embryos during in vitro fertilization (IVF) procedures.

Edouard Van Beneden published a paper in 1875 in which he first mentions the pronucleus by studying the eggs of rabbits and bats.

Van Beneden also found that the sperm enters into the cell through the membrane in order to form the male pronucleus.

When the male pronucleus is formed, after the sperm cell reaches the egg, the two pronuclei migrate towards each other.

[7] In sea urchins, the formation of the zygote starts with the fusion of both the inner and outer nuclei of the male and female pronuclei.

It is unknown if one of the pronuclei start the combination of the two, or if the microtubules that help the dissolution of membranes commence the action.

[9] When vinblastine is added to the ovum, there is a high rate of pronuclear fusion failure.

In mammalian egg cells, the chromatin from the pronuclei form chromosomes that merge onto the same mitotic spindle.