Findings of Morgan in chicken: are they real?

The genetic sex determination of Gallinaceae was explained in literature on the chromosomallevel by the existence of the male sex, homogametic ZZ, and of the female sex, heterogametic ZW, aswell as by the existence of genes within the chromosome Z and by the absence of genes within thechromosome W (Morgan 1919). In this paper we present the experimental results of direct and reciprocalgenetic recombination. The experimental design allows the identification of the dominant sex gene linkedto the gene that determines the plumage color in the first generation females. Both these genes arelocated within the chromosome W. In the same generation the recessive sex gene was identified withinthe chromosome Z. The second generation was obtained by cross of the males and females of the firstgeneration. In each category of genotypes of the second generation males and females are displayedequally. Three categories of genotypes were produced, namely dominant homozygous, heterozygous,and recessive homozygous. The experimental results demonstrate that within the chromosome W boththe dominant sex gene and the gene transmitting the plumage color are located. Our results are not inaccordance with the hemizygotic theory of Morgan (1919).