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I know that hybrid animals like mules are infertile. What about clones? Do cloned animals show the same fertility as their original?

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  • $\begingroup$ Do you know why hybrid animals are infertile? $\endgroup$ – Cell Oct 15 '18 at 16:22
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    $\begingroup$ @Cell Have you ever noticed that some people have a tendency to answer a question with another question? $\endgroup$ – Imprisoned Rhesus Oct 15 '18 at 16:24
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    $\begingroup$ @ImprisonedRhesus Answering questions with other questions can be a good pedagogical technique, since those questions are meant to guide your logical thinking while allowing you some creativity (i.e., without giving away the answer too directly). $\endgroup$ – Bryan Krause Oct 15 '18 at 16:29
  • $\begingroup$ Also as a curiosity - mules are typically infertile, but there are dozens of well-documented cases of mules and hinnies that have successfully reproduced, so it's not an all-or-nothing thing. $\endgroup$ – iayork Oct 15 '18 at 18:04
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    $\begingroup$ @iayork You should be more cautious before calling other people snarky and a bully. The original poster was implying that clones may be infertile for the same reasons that hybrids are otherwise why even bring it up? I know that the topics are completely unrelated hence I wanted to gauge how much the original poster knows before answering. Unlike your verbose, jargon filled, one-size-fits-all answer, I like to answer with the knowledge and expertise of the asker in mind. $\endgroup$ – Cell Oct 15 '18 at 20:14
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Cloned animals, at least in the first generation, are often subfertile and have lower viability than their progenitors. The reasons for this are complicated but often are related to epigenetic changes that lead to altered gene regulation.

Further reading:

Although the technology of SCNT has been applied successfully by many research teams, some SCNT animals have abnormal or lethal phenotypes, including facial abnormalities, pulmonary hypertension [3], contracted tendons [9], low birth weight [10, 11], as well as distinct depigmentation of the skin and hair ... Based on previous studies, insufficient epigenetic reprogramming of somatic donor cells may result in phenotypic abnormalities in the offspring ...

--Dysregulation of genome-wide gene expression and DNA methylation in abnormal cloned piglets

The epigenetic state of the ES cell genome was found to be extremely unstable. Similarly, variation in imprinted gene expression was observed in most cloned mice, even in those derived from ES cells of the same subclone. Many of the animals survived to adulthood despite widespread gene dysregulation, indicating that mammalian development may be rather tolerant to epigenetic aberrations of the genome.

--Epigenetic instability in ES cells and cloned mice.

Because few clones survive to birth, the question remains whether survivors are normal or merely the least severely affected animals, making it to adulthood despite harboring subtle abnormalities originating from inadequate nuclear reprogramming ... Our results suggest that many expression abnormalities are common to the NT procedure whereas some reflect the particular donor nucleus. These results further emphasize the severity of placental dysfunction and illustrate abnormalities in clones surviving to birth.

--Abnormal gene expression in cloned mice derived from embryonic stem cell and cumulus cell nuclei

Although clone D had a poorer libido and entered puberty later than those of the other cloned male cats, he produced gonadal hormones within the average range. Four of the cloned male cats had normal fertility.

--Reproductive fertility of cloned male cats derived from adult somatic cell nuclear transfer.

(Note that this paper concluded that the cloned male cats had "normal fertility", but one of four (25%) had reproductive abnormalities (reduced libido and delayed puberty); the numbers are too small for anything definite but I would say this is evidence for abnormal fertility, not the reverse)

Some early papers do claim normal fertility of cloned mice, but those are simply based on the fact that the cloned mice could have offspring (i.e. were not completely infertile) and didn't actually compare fertility of cloned vs. "normal" laboratory mice.

  • Wakayama, T., Perry, A.C.F., Zuccotti, M., Johnson, K.R. & Yanagimachi, R. Full-term development of mice from enucleated oocytes injected with cumulus cell nuclei. Nature 394, 369–374 (1998).
  • Wakayama, T. & Yanagimachi, R. Cloning of male mice from adult tail-tip cells. Nature Genet. 22, 127–128 (1999).
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