Q23 - Oocyte Attrition, Ovulation Fraction, and Maternal-Age Risk of Down Syndrome
The oocytes in the human ovary are most numerous in the 5-month-old fetus (approximately 7 million), then
decrease rapidly to about 2 million at birth. : birth. : menarche.
Figure 1.
Using the information and data, determine which of the statements are true or which are false.
Q23-1. The number of germ cells decreased by 70% at birth because the oocytes die during the period of meiosis II.
Q23-2. The number of oocytes that are ovulated during menstrual periods is less than ___ of the germ cells surviving at menarche.
Q23-3. The risk of Down syndrome increases with the age of the mother. Choose the most appropriate reason for this.
Question reproduced from IBO 2020, Theoretical Exam 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)