Complete molar pregnancy is one where an ovum devoid of nucleus is fertilized by a sperm after which the haploid set of chromosomes double to form a diploid set.

As far as my understanding extends if the sperm had Y chromosome the embryo will not survive.

However if the sperm has X chromosome the zygote will survive to have the 46 XX karyotype and will start to grow as molar pregnancy (which is basically trophoblastic tissue with no fetal parts, as answered by Anongoodnurse).

Why is there no proper fetus? Why can't a "female clone" of male parent form instead? Where is the defect as such?

The Question pointed out by WYSISYG contains data only from animal studies. Although it answers my question, I want more data obtained from study of human trophoblastic tissue (from the molar pregnancy). Papers on imprinting which are linked in those questions have no mention of molar pregnancy although Prader-Willi and Angelman syndromes are mentioned (as cases seen in humans).

Oops, I corrected my question thanks to anongoodnurse. I mixed up complete and partial moles with each other.


1 Answer 1


"However if the sperm has X chromosome the embryo will survive to have the 46 XX karyotype and will start to grow as molar pregnancy."

Complete molar pregnancy is diploid, and there is no fetal tissue identifiable. It is a disease of the placenta, a uterine tumor (cancerous in some cases, non-cancerous in others); fetuses do not develop from such pregnancies, not haploid or diploid (though they are usually 46, XX). A male haploid 23,X replicates, but only trophoblastic (what should be the placenta) tissue results.

Partial molar pregnancies are triploid, and a fetus can sometimes be identified. However, it is non-viable, as polyploidy is non-viable in humans. Even if it were, the abnormal placenta could not support it.

Molar Pregnancy
p57KIP2 immunohistochemistry in early molar pregnancies: emphasis on its complementary role in the differential diagnosis of hydropic abortuses

  • $\begingroup$ This should be a comment rather than answer. It does not answer the question in any way. $\endgroup$
    – One Face
    Mar 1, 2015 at 1:24
  • $\begingroup$ Yes this should be converted to comment. $\endgroup$
    Mar 1, 2015 at 6:16

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