Confirmation of the first intronic sequence in the bivalvian mitochondrial genome of <i>Macoma balthica</i> (Linnaeus, 1758).

In 2020, the first male-type mitochondrial genome from the clam <i>Macoma balthica</i> was published. Apart from the unusual doubly uniparental inheritance of mtDNA, scientists observed a unique (over 4k bp long) extension in the middle of the <i>cox2</i> gene. We have attempted to replicate these data by NGS DNA sequencing and explore further the expression of the long <i>cox2</i> gene. In our study, we report an even longer <i>cox2</i> gene (over 5.5 kbp) with no stop codon separating conserved <i>cox2</i> domains, as well as, based on the rtPCR, a lower relative gene expression pattern of the middle part of the gene (5' = 1; mid = 0.46; 3' = 0.89). Lastly, we sequenced the <i>cox2</i> gene transcript proving the excision of the intronic sequence.