MadSci Network: Development

Re: Parthenogenesis involves using an egg/ovum. How does a diploid ovum form?

Date: Wed Feb 13 09:41:22 2002
Posted By: Paul Szauter, Staff, Mouse Genome Informatics, The Jackson Laboratory
Area of science: Development
ID: 1013406612.Dv

You have asked a really great question. We all know that sperm and eggs are 
haploid, so where does the other genome come from?

Actually, eggs of mammals and many other types of animals do not complete 
the meiotic divisions until late in their development. In Drosophila (fruit 
fly), the two meiotic divisions occur only after fertilization. Mammalian 
eggs initiate meiosis while the female embryo is still developing, then 
arrest in prophase of meiosis I. In humans, they can remain in this state 
for forty years! Near the time of ovulation, primary oocytes complete 
meiosis I, ejecting half of their genetic material as the first polar body. 
In most vertebrate species, meiosis II is not completed until after 

Please see:

So the answer to your question is that you can essentially trick the 
secondary oocyte into using the genetic material that would have been 
ejected in the second polar body as the equivalent of a sperm nucleus. 
Meiosis produces four haploid products (easier to see in sperm development), 
so a regular embryo gets one haploid genome from the sperm and one from the 
egg. A parthenote gets two haploid genomes by getting (essentially) one from 
what would have been the egg pronucleus and one from what would have been 
the second polar body.

Here is a news account of parthenogenesis in monkey cells:

The original article is Science:

Science 295: 779-780 (2002) [news and comment]


Science 295: 819 (2002)

The treatments that induce parthenogenesis include electroporation and 
inhibition of protein synthesis or phosphorylation using drugs. Eggs can 
also be treated with MPF (maturation promoting factor) inhibitors. Please 

Biol Reprod 2001 Jul;65(1):253-9

You may also find this Glossary useful:


Paul Szauter
Mouse Genome Informatics

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