Fig. 5

Evolution of intron 12 length and models for the origin of imprinting in IGF2R. a The marsupial-specific elongation of intron 12 length in IGF2R. Length of the bars represents IGF2R intron 12 lengths in each species. The multiple colours in the bars show rates of transposable elements in intron 12 sequences that were calculated by RepeatMasker (www.repeatmasker.org). Blue; SINEs, Red; LINEs, Green; LTR elements, Purple; DNA elements, Light blue; unmasked unique sequences. b Two hypotheses for the origin of imprinting in IGF2R. Left; the origin of imprinting of the IGF2R locus was just the once in the common ancestor of eutherians and marsupials, and the change of DMR location to intron 12 and consequent loss of former DMR in intron 2 have been occurred in the marsupial ancestor. Right; the acquisition of IGF2R imprinting has been independently occurred in both eutherian ancestor and marsupial ancestor