Reduced oocyte numbers in tertiary trisomic mice with male sterility.

Oocyte counts carried out in 3- to 5-day-old tertiary trisomic Ts(5(12))31H mice revealed a mean reduction of 71% in the number of oocytes as compared with that of normal littermates. The pool of small oocytes was reduced by 75%, and the number of growing oocytes by 8%. The sperm count of the trisomic males was less than 1% of normal, with most spermatozoa being abnormal (Beechey et al., 1980). These results indicate that the presence of the extra 5(12) chromosome, which causes male sterility, also has a marked effect on oogenesis. Possible reasons for the difference in severity of the gametogenic impairment in males and females are discussed.