Oocyte Development and Responses to Radiation Effects

Essential in the analysis and interpretation of fertility results is a knowledge of the nature of the mouse ovary. The total reproductive capacity procedure, as already stated, covers the study of fertility effects throughout the entire posttreatment reproductive life-span of females. At the time of treatment, all germ cells with the exception of those that will be ovulated within a few hours (Russell and Russell, 1955) are at the primary oocyte state—specifically, at diffused diplotene. The arrest of all germ cells at this meiotic state occurs shortly after birth. The majority of the oocytes of young adults are morphologically still the same small oocytes found arrested after birth they are small, primordial oocytes 

For single acute treatment, two groups of young adult female mice (about 10-13 weeks old) each from two strains are given a single dose of the test chemical. Immediately after treatment each female of one group 

FIGURE 1. Fertility throughout reproductive life-span of female mice treated with the chemicals shown. 

The second group of female mice is subjected to the dominant lethal mutation test. This test is necessary not only to analyze effects of chemicals on early litters but also because a small effect on fertility which might be detectable by an increase in dead implantation, for example, may not show up in the average size of first litters of females being tested for total reproductive performance. Females in the dominant lethal study are caged individually with untreated males on the day of treatment and are 

TABLE 1. Reproductive Performance of Chemically Treated Female Mice 

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