Analysis of MIR frequency in dog and opossum immune defense genes. MIR sequences were divided into mammalian-wide and metatherian/monotremata-specific. Immune response genes displayed significantly higher frequencies of both MIR types compared to the remaining genes. Box height represents sample interquartile range and the bold line depicts the median position. The whiskers extend to the most extreme data point, which is no more than 1.5 times the interquartile range from the box.