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UCSB Science Line (University of California, Santa Barbara, scientist q/a) claims that:

Long before we are born, the same gonads either become testes, if the embryo has a Y chromosome, or ovaries if it doesn’t. Once that process starts, other changes happen that tell the testes to make sperm and the ovaries to make eggs. There are some rare cases where only one of the gonads gets the message from the Y chromosome, or only part of the gonads gets that message. In that case, an individual can make both eggs and sperm.

However, based on my searches, I haven't been able to find any further support or documentation for this claim. When this was asked on reddit, answers claimed it does not appear there has ever been a documented case, for example.

If what UCSB Science Line claims is true, I'd think it certainly would be documented somewhere. Has there ever been such a case or cases documented?

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    Males with persistent Müllerian duct syndrome can have ovaries (as well as testes), but I can't find anything that specifically says they can produce eggs.
    – Gordon Davisson
    Apr 16, 2022 at 10:54
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    @User65535 by going through wikipedia links and then this published research I did find this case which does sound like it would fit my description. It says it seems ovulation had occurred, and the individual did father a child.
    – eis
    Apr 16, 2022 at 12:42
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    From the POV of a biologist (and just FYI), the main issue here of course is that it is not as simple as "a message" that is received or not. We are talking about a complex development from the embryo all the way through puberty. One being triggered, furthered, and controlled by a sequence of hormones and other assorted biochemistry. Much of the development being more or less mutually exclusive. So it takes a person that has many things going quite wrong biochemically, but at the same time so "right" that both pathways are taken... the chances against that happening are astronomical.
    – DevSolar
    Apr 20, 2022 at 15:40

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Yes, but it is spectacularly rare, and the one documented case I have found was not "one of the gonads gets the message", but a case of male/female chimerism or less likely mosaicism. Also it is considered unlikely that both occurred at the same time.

A review of 283 cases of human true hermaphroditism found only two cases of proven spermatogenesis. One of these patients was noted as having ovulation and further fathered a child, and was considered the first in 1982.

An unusual case of true hermaphroditism is reported. The patient was a 32-year-old phenotypically male true hermaphrodite. Histology of his removed ovary suggested that ovulation had, at some time, occurred. He had also fathered a child and this is believed to be the first case of a cytogenetically proved true hermaphrodite who is fertile as a male.

As has been shown, the ovary in this case was relatively normal with perhaps a little more fibrous stroma than is usual. Ovulation was assumed to have occurred at some time given the presence of corpora albicantes. These only occur in the presence of ovulation since they develop from the involuting corpora lutea.

The presence of oogenesis and spermatogenesis at the same time is unlikely, and in this case the testosterone was in the high normal range. One must therefore postulate that, if both were not proceeding at the same time, ovulation had occurred in the past, possibly before testicular maturation.

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  • So biologically speaking, did the individual have one teste, and one ovary, or did he have two pairs? if it's the later, did they share the same DNA? I'm curious if it's a fused twin, or something else.
    – tuskiomi
    May 11, 2022 at 16:49
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    The individual had one testis and one ovary (the ovary was removed prompting the paper). Exactly what the etiology was in not certain. it is thought they were a chimera, ie. fused twin.
    – User65535
    May 13, 2022 at 10:47
  • @tuskiomi the singular of testes is not teste but testis.
    – phoog
    May 13, 2022 at 21:18
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https://pubmed.ncbi.nlm.nih.gov/19344081/

Abstract We report a healthy and unambiguously female newborn, whose phenotypic sex contradicted the expected male sex based on previously performed prenatal cytogenetic analysis. Both 46,XX and 46,XY cells were detected in a villus sample, the former having been attributed to maternal cell contamination. Postnatal karyotyping in peripheral lymphocytes confirmed the presence of two cell lines, one 46,XX (70%) and one 46,XY (30%). After exclusion of alternative explanations for the observed genotype, a diagnosis of chimerism was made. Chimeras containing cell lines of opposite sex usually feature ovotesticular development with associated genital ambiguity. To account for the normal female appearance of our patient, we postulate the exclusive involvement of 46,XX cells in gonad formation.

The clinical and genetic heterogeneity of mixed gonadal dysgenesis: does "disorders of sexual development (DSD)" classification based on new Chicago consensus cover all sex chromosome DSD?-- [https://pubmed.ncbi.nlm.nih.gov/22644991/][1]

  [1]: https://pubmed.ncbi.nlm.nih.gov/22644991/
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    Unless I'm misreading it, this doesn't mention sex cells (sperm and eggs) at all. Indeed, it seems to be saying the patient presented exclusively with normal female gonads.
    – IMSoP
    May 1, 2022 at 0:20
  • It doesn't but both are possible as products despite the presence of either or both sex chromosomes even both are sometimes present in some Disorders of sez development. What is on the exterior may appear to be male in some disorderders, but begin menarche at puberty, so what is in the interior clearly doesn't match though menses means ovulation while sperm may be produced by working testes also even as much as it would seem improbable. Does this meet you're requirement as an answer acceptable enough?
    – James Butler
    May 2, 2022 at 2:28
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    Welcome to Skeptics! The question was rather specific, asking for production of both kinds of sex cells, which User65535 answered in the affirmative. Your answer is about a related, and certainly interesting, case of an individual that apparently has not yet produced any sex cells on behalf of it being an infant. I.e., this does not answer the question, and does not add to the answer already present, sorry.
    – DevSolar
    May 2, 2022 at 6:19
  • I specifically said this is possible in a genetically xx/xy mosaic genetic pattern, but let me spell out that one with this mosaic can have one ovaRY well as a working testicle so both possible cells can be there. I thought disorders of sec development relevant.adding to the conversation, I don't think I was stepping out of line to bring the information to the thread. It does nothing to diminish my place in the Skeptic area on Stack,, and in fact adding more information t on this is what good Skeptics do., as it can lead to new conversation. Publicly shaming wasn't right. Won't be able again.
    – James Butler
    May 3, 2022 at 18:28

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