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