If one follows 130 primary oocytes in an animal through their various stages of oogenesis, how many secondary oocytes would be formed?
The correct answer and explanation is:
Correct Answer: 130 secondary oocytes
Explanation:
In female animals, oogenesis is the process through which mature egg cells, or ova, are formed. This process starts with primary oocytes, which are diploid cells (2n). Each primary oocyte undergoes the first meiotic division, resulting in two unequal cells: a secondary oocyte and a first polar body.
The division is unequal in terms of cytoplasm. The secondary oocyte receives the bulk of the cytoplasm to support future development, while the polar body is much smaller and typically degenerates. Importantly, only one secondary oocyte is produced from each primary oocyte during the first meiotic division.
If you begin with 130 primary oocytes, and each one produces only one secondary oocyte, then the total number of secondary oocytes formed is:
130 primary oocytes × 1 secondary oocyte each = 130 secondary oocytes
The secondary oocyte then begins the second meiotic division but halts in metaphase II unless fertilization occurs. If fertilization does take place, the secondary oocyte completes meiosis II to form an ovum and a second polar body. However, the question focuses only on the number of secondary oocytes, not the final ova or polar bodies.
Therefore, no matter what happens after this point, each primary oocyte gives rise to one secondary oocyte, making the total number of secondary oocytes 130 from 130 primary oocytes. This calculation is based on the biological rule that meiosis I in oogenesis results in one secondary oocyte per primary oocyte.