pronucleus (redirected from pronuclei)

pronucleus /pro·nu·cle·us/ (-noo´kle-us)

1. the precursor of a nucleus.

2. the haploid nucleus occurring after meiosis in a germ cell.

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pro·nu·cle·us (pr-nkl-s)

n.

1. One of two nuclei undergoing fusion in karyogamy.

2. The haploid nucleus of a sperm or egg before fusion of the nuclei in fertilization.

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pronucleus

[-no̅o̅′klē·əs] pl. pronuclei

Etymology: Gk, pro + L, nucleus, nut kernel

the nucleus of an ovum or a spermatozoon after fertilization but before fusion of the chromosomes to form the nucleus of the zygote. Each pronucleus contains the haploid number of chromosomes, is larger than the normal nucleus, and is diffuse in appearance. The pronucleus of the ovum is formed only after it has completed its second meiotic division and the second polar body has formed, which occur after the spermatozoon has penetrated. It then loses its nuclear envelope, releasing the chromosomes so that synapsis with the chromosomes of the male pronucleus, which is contained in the head of the spermatozoon, can occur. Also called germinal nucleus, germ nucleus. See also oogenesis, spermatogenesis.

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pronucleus

pl. pronuclei; the haploid nucleus of a sex cell.

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female pronucleus

the haploid nucleus of the fully mature ovum which loses its nuclear envelope and liberates its chromosomes to meet the synapsis with those from the male pronucleus.

male pronucleus

the nuclear material of the head of a spermatozoon, after it has penetrated the ovum and acquired a pronuclear membrane.