Allelic imbalance is a prevalent and tissue-specific feature of the mouse transcriptome

We perform a systematic classification of allelic imbalance in mouse hybrids derived from reciprocal crosses of divergent strains. We observe that deviation from balanced biallelic expression is common, occurring in ~20% of the mouse transcriptome. Allelic imbalance attributed to genotype is by far the most prevalent class and typically is tissue-specific. However, some genotype-based imbalance is maintained across tissues and is associated with greater genetic variation, especially in 5’ and 3’ termini of transcripts. We further identify novel random monoallelic and imprinted genes, and find that genotype can compete with parental origin even in the setting of large imprinted regions. PolyA-selected RNA-sequencing in F1 hybrid and parental cells of Mm. musculus and Mm. castaneus origin