Fig. 1. Inheritance patterns in Varroa destructor mites show that males inherit two alleles from their mother and transmit both alleles to their daughters with equal probability. Females are produced sexually.

For each of the two cross types, we first filtered for informative genotypes in F0 and F1 and then observed the genotypes of those sites in F2 females and males, to infer the mode of genetic inheritance. a,c show the genotype flow for representative families (families 478 and 534, respectively) over three generations along the largest chromosome (NW_019211454) (“F0-F2 one family, one chromosome”). In cross 1 (panel A), the F0 female was homozygous (AA), and her F1 offspring were a heterozygous female (AB) and a homozygous male (AA). This filtering yielded 33 sites, whose genotypes were then observed in the F2 female and male offspring. In cross 2 (c), the F0 female was heterozygous (AB), and her F1 offspring were a homozygous female (AA) and a heterozygous male (AB). This filtering yielded 14 sites, whose genotypes were then observed in the F2 female and male offspring. b,d (“F2 pooled families, all sites”) show pooled genotype proportions in F2 females and males across all families and all seven chromosomes for cross 1 (AB × AA; panel B) and cross 2 (AA × AB; D). In both crosses, F2 females showed an approximately 1:1 ratio of AA:AB genotypes, consistent with sexual reproduction, whereas F2 males predominantly inherited their mother’s genotype, indicating obligatory maternal inheritance. As expected from AA × AB crosses, no BB genotypes were observed. Colors: yellow = AA, green = AB, blue = BB. F0 males were not collected; therefore, their genotypes are unknown and shown in gray.