Figure 1. Origin and inheritance of mtDNA in cyprinid fishes.

(a) Goldfish red variety and blunt-snout bream used for reciprocal hybridization. (b) Scheme of PCR primers for cytb and tfam, showing primers specific to goldfish (open arrowhead) or blunt-snout bream (grey arrowhead) and common to both species (black arrowheads). For more details see Figs S1 and S2. (c,d) Specificity and sensitivity of mtDNA detection by PCR. Genomic DNA mixtures between goldfish and the blunt-snout bream were prepared at various ratios and used for PCR analysis by using species-specific cytb primers. Notably, an amount as low as 1‰ is easily detectable. (e) PCR analysis of mtDNA origins, showing the absence of sperm cytb in the hybrid larvae between female goldfish and male blunt snout bream and the coexistence of maternal and paternal cytb in the zygotes from reciprocal hybridization. Asterisks depict sperm mtDNA. DNA was isolated from 20 pooled zygotes and embryos at each stage from parental species and reciprocal hybridization and analyzed by PCR at representative stages indicated. β-actin was used as a loading control. PCR and gels were run under the same conditions. B, blunt-snout bream; G, goldfish; BG, blunt-snout bream female × goldfish male; GB, goldfish female × blunt-snout bream male.