Nondisjunction and Polyploidy

In the silkworm, availability of egg-color genes as genetic markers made it possible to design a unique system for the detection of nondisjunction and polyploidy. Since the phenotype of the zygote is expressed in the serosa color of the egg, the detection of these exceptions can be performed without raising Fi larvae. 

Using this system, experiments have been performed to induce nondisjunction with X rays, organic mercury compounds, MMC, and CO2 gas treatment. The data are summarized in Tables 2 and 3. 

In the first group, treatment with both kinds of mercuric compounds increased the incidence of wild type with increasing doses, but in the II B group of Table 3, treatment with saline only yielded a very high frequency. Further experiments on the dose-frequency relationship showed that the frequency did not necessarily increase with increase of the administered dose. Genetic analysis of the wild-type individuals indicated that these exceptional were mainly triploids (Table 4). 

A total of 113 females and 6 males were analyzed. The former included 3 4n, 102 3n, and 8 2n females. Among the latter, 5 2n males were confirmed as the products of chromosomal recombination. Other experiments, in which genetically marked sex chromosomes were used and X rays and high-tempera- 

TABLE 2. Experimental Results on the Induction of Nondisjunction I. Injection 3 Days before Emergence 

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