1. Department of Zoology, University of Maryland, College Park, Maryland 20742, USA
2. Department of Biology, University of Rochester, Rochester, New York 14627, USA

Correspondence to: Gerald S. Wilkinson¹ Correspondence and requests for materials should be addressed to G.S.W. (e-mail: Email: wilkinson@zool.umd.edu).

In some species, females choose mates possessing ornaments that predict offspring survival^{1, 2, 3, 4, 5}. However, sexual selection by female preference for male genetic quality^{6, 7, 8} remains controversial because conventional genetic mechanisms maintain insufficient variation in male quality to account for costly preference and ornament evolution^{9, 10}. Here we show that females prefer ornaments that indicate genetic quality generated by transmission conflict between the sex chromosomes. By comparing sex-ratio distributions in stalk-eyed fly (Cyrtodiopsis) progeny we found that female-biased sex ratios occur in species exhibiting eye-stalk sexual dimorphism¹¹,¹² and female preferences for long eye span¹³,¹⁴. Female-biased sex ratios result from meiotic drive¹⁵, the preferential transmission of a 'selfish' X-chromosome. Artificial selection for 22 generations on male eye-stalk length in sexually dimorphic C. dalmanni produced longer eye-stalks and male-biased progeny sex ratios in replicate lines. Because male-biased progeny sex ratios occur when a drive-resistant Y chromosome pairs with a driving X chromosome¹⁵, long eye span is genetically linked to meiotic drive suppression. Male eye span therefore signals genetic quality by influencing the reproductive value of offspring¹⁶.