The full-length (i. e., containing the entire protein-coding region) cDNA for a specific eukaryotic gene in humans is 1500 nucleotides long. You screen a pig genomic library with this cDNA and isolate two genomic clones of different lengths. Both clones are sequenced and found to be 1900 and 2100 nucleotides long from start codon to stop codon. Screening of genomic libraries of several other organisms reveals that all of them contain only one genomic clone -- pigs seem to be the exception to the rule here. What evolutionary events might have led to the presence of two genomic clones in pigs, and the discrepancies in their length compared to the cDNA probe