This account of how sable was purified shows how difficult it is to separate two recessive factors that give closely similar somatic effects. If a character like sable should be present in any other black stock, or if a character like black should be present in sable, very erratic results would be obtained if such stocks were used in experiments, before such a population had been separated into its component races. Sable males of the purified stock were mated to wild females and gave wild-type (gray) males and females. These inbred gave the results shown in table 6. No sable females appeared in F_2, as seen in table 6. The reciprocal cross gave the results shown in table 7. {35} The F_1 males were sable like their mother. The evidence thus shows that sable is a sex-linked recessive character. Our next step was to determine the linkage relations of sable to certain other sex-linked gens, namely, yellow, eosin, cherry, vermilion, miniature, and bar. TABLE 6.--_P_1 wild [female] [female] x sable [male]. F_1 wild-type [female] [female] x F_1 wild-type [male] [male]._ +---------------+-------------------+-------------------+---------------+ | | | | | | Reference.[4] |Wild-type [female].| Wild-type [male]. | Sable [male]. | | | | | | +---------------+-------------------+-------------------+---------------+ | | | | | | 88 C | 218 | 100 | 70 | | 143 C | 245 | 108 | 72 | | 146 C | 200 | 115 | 82 | | +-------------------+-------------------+---------------+ | Total | 663 | 323 | 224 | | | | | | +---------------+-------------------+-------------------+---------------+ TABLE 7.--_P_1 sable [female] x wild [male] [male]. F_1 wild-type [female] x F_1 sable [male]._ +--------------+-------------+-------------+-------------+-------------+ | | | | | | | Reference. | Wild-type | Wild-type | Sable | Sable | | | [female]. | [male]. | [female]. | [male]. | +--------------+-------------+-------------+-------------+-------------+ | | | | | | | 4 I | 10 | 10 | 6 | 10 | | | | | | | +--------------+-------------+-------------+-------------+-------------+ LINKAGE OF YELLOW AND SABLE.