Inheritance of Age at Sexual Maturity

Dr. RAYMOND PEARL (1912) was the first worker to suggest that sexlinked factors were involved in the inheritance of fecundity. PEARL used as a measure of fecundity the eggs produced during the winter period. He proposed that two major dominant factors were responsible for high egg production, one of which resided in the sex chromosome. GOODALE (1919) and HURST (1921) each failed to confirm the earlier statement of PEARL that a sex-linked factor was involved in the inheritance of fecundity. GOODALE (1919) called attention to the inadequacy of PEARL’S method of attacking the problem of the inheritance of fecundity. He pointed out that there were a number of more or less independent genetic factors responsible for high egg production and that PEARL’S method of considering as a unit the total number of eggs produced could not be expected to yield critical results. GOODALE (1922) held that the annual egg record was dependent upon the combined action of the following five characteristics : maturity, intensity, broodiness, persistency, and winter pause. HAYS (1924) proposed that maturity (age a t sexual maturity) was dependent upon two pairs of factors, one of which was sex-linked. He held that the early maturity factor was dominant in each case. The data presented in support of the theory are rather meager. HAYS has suggested that since PEARL’S study of inheritance of fecundity utilized only egg production during the winter period, he was probably considering primarily age at sexual maturity. It is readily seen that differences in age a t which birds started to lay would materially influence the number of eggs produced in that period. PUNNETT (1930) outlined what he considered a crucial test for the theory of PEARL that sex-linked factors were involved in the transmission of high fecundity. It had been shown previously that the two genes, silvergold and barred-non-barred were located on the sex chromosome about 45 units apart (AGAR 1924, SEREBROVSKY and WASSINA 1927, WARREN 1928). PUNNETT stated that if these two genes and the one for fecundity were all on the sex chromosome, through segregation some evidence for linkage among them should be found. In following the segregation of these