If, however, a new mutant type does not show this sex-linked inheritance, its chromosome is determined by taking advantage of the fact that in Drosophila there is no crossing-over in the male between factors in the same chromosome. These results depict that the yellow body y and sepia eyes se alleles do not follow Mendelian genetic theory and do not conform to the ideal ratios of phenotype inheritance. Again, just to be sure we don't overlook something interesting, we will perform the cross both ways--with white-eyed males, or with white-eyed females. It is thus impossible to assume that the X sperms are normally female-producing because of something else than the X or that the Y sperm produce males for any other reason than that they normally fertilize X eggs. McEwen, shows clearly that there are fewer than the normal number of mature eggs, recalling the case of rudimentary. If they receive the recessive allele, they will express the recessive trait. Males are red-eyed because they only have one copy of the gene and that copy is for the red allele. Whatever the nature of the lethals' action, it can be shown that from among the offspring obtained from certain stocks expected classes are missing, and the absence of these classes can be accounted for on the assumption that there are present mutant factors that follow the Mendelian rule of segregation and which show normal linkage to other factors, but whose only recognizable difference from the normal is the death of those individuals which receive them. The rudimentary females mate in the normal time with rudimentary or with normal males, and their sexual behavior is normal. So far as we can see, there is no reason to suppose that the mutations which can be described as superficial are disproportionally more likely to occur than others. The image on the right is hosted at http: The only effect which the extra Y has is as an extra wheel in the machinery of synapsis and reduction; for, on account of the presence of the Y, both X's of the XXY female are sometimes left within the ripe egg, a process called secondary non-disjunction. The list at the top of page 21 gives the names of the factors dealt with in this paper. The y strain exhibited a light, creamy-yellow colored body color but iridescent red wild type WT eyes. As far as sex is concerned this is a perfectly normal female. If we think of a chromosome as made up of a chain of chemical particles, there may be a number of possible recombinations or rearrangements within each particle.