# Why is the DRAGEN Array VCF output for mitochondrial loci showing only 0 or 1 in the GT field?

Mitochondrial DNA is treated as haploid in DRAGEN Array, which is why the genotype (GT) calls for mitochondrial loci are reported as either 0 or 1.

In human genomics and clinical genetics, mitochondrial DNA is treated as a haplotype (a single maternal lineage sequence) rather than a diplotype. Because mitochondrial DNA (mtDNA) is inherited exclusively from the mother (uniparental, non-recombining) with no second parental copy, each individual’s mitochondrial genome is recorded as one set of variants (one haplotype).

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