Humans easier to clone than sheep

All non-primate mammals can develop 'large offspring syndrome' when cloned because they have only one functional copy of insulin-like growth factor II receptor (M6P/IGF2R). This is due to a rare phenomenon known as genomic imprinting, in which the M6P/IGF2R gene is stamped with markings that turn off its function. But in August Human Molecular Genetics Keith Killian and colleagues from Duke University Medical Center show that in humans, genomic imprinting for M6P/IGF2R does not occur, theoretically making humans technically easier to clone than sheep and other nonprimates.

Killian et al. used six different single-nucleotide polymorphisms to test for M6P/IGF2R imprinting in embryonic tissue from 75 human conceptuses and 12 term placentas and, surprisingly, they observed unambiguous biallelic M6P/IGF2R expression in each sample (Hum Mol Genet 2001, 10:1721-1728). They suggest that because humans — unlike nonprimates — have two functional copies of the M6P/IGF2R gene, it is unlikely...