Pronuclei is plural for pronucleus.

Description

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A procucleus is a nucleus with a haploid number of chromosomes (23 in humans). In the fertilization process, the pronucleus of the female cell (oocyte, or egg) and the pronucleus of the male cell(sperm) fuse together to form a normal diploid number of chromosomes (2N = 46 in humans).

The appearance of two pronuclei (2pn) is the first sign of successful fertilization as observed during IVF cycle and is usually observed 18 hours after insemination or ICSI.