Chromosomally Abnormal Gametes as a Cause of Developmental and Congenital Anomalies in Humans *

Human gamete chromosome studies using 702 oocytes and 15,864 spermatozoa were reviewed. These studies were chosen because they were carried out with our improved chromosomal technique, the gradual fixation‐air drying method, which has been proven to be very reliable. The incidence of aneuploidy was about eight times as high in the oocytes (11.0%) as in the spermatozoa (1.4%), whereas that of structural chromosome aberrations was three times as high in the spermatozoa (14.1%) as in the oocytes (4.7%). In the spermatozoa, segregation errors leading to aneuploidy were found randomly among eight chromosome groups (A‐G and sex chromosome). In contrast, they did not occur randomly in the oocytes. The observed frequency was significantly higher in group G and significantly lower in group A, as compared with the theoretical frequencies which were calculated according to the assumption that the segregation errors had taken place with an equal chance in each of 23 chromosomes. About 60% of the segregation errors were found to be due to so‐called nondisjunction (loss or gain of dyads) and about 40% were due to so‐called predivision (loss or gain of monads). The incidence of aneuploid oocytes increased slightly with the increase of donor age, although showing no statistical significance. The incidence of spermatozoa with structural chromosome aberrations vaned considerably from donor to donor (3.6–24.8%). However, there was no positive correlation between the occurrence of these spermatozoa and the age of donors or the habit of smoking. Incidences of chromosome aberrations in the human gametes (22.8% in oocytes and 15.5% in spermatozoa) were far higher than those in experimental animals. These seem to be associated closely with the characteristics of human reproduction and are responsible for a great part of human embryonic loss and developmental anomalies.