Related Experiment Video
Updated: May 15, 2026

Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination
Published on: July 18, 2025
A study of meiotic segregation in a fertile human population following ovarian stimulation with recombinant FSH-LH
Esther Velilla1, Silvia F Fernández, Jordi Suñol
1Institut Marquès, C/Manuel Girona no. 33 La Masia-Clínica CIMA, Barcelona, Spain. esther.velilla@institutomarques.com
Objective:
The aim of the study is to investigate the meiotic segregation in fresh eggs from anonymous egg donors and to analyze the baseline levels of aneuploidy in this population.
Results:
The study includes the largest series of donor eggs so far studied: 203 eggs from donors aged between 20 and 31 years. No diagnosis was obtained in 10.8 % of cases (22/ 203). The biopsy of the first and second polar bodies was completed in a sequential manner on day 0 and day 1 of embryo development. Chromosomes 13, 16, 18, 21 and 22 are analyzed by means of the FISH test. The diagnosable fertilized eggs gave an aneuploidy rate of 19.1 % (31/162), with 83.8 % (26/31) of the errors produced during meiosis I, 12.9 % (4/31) produced during meiosis II, and 3.2 % (1/31) produced during both meiosis I and II. The premature division of sister chromatids is the main source of meiotic error during Meiosis I, resulting in the creation of oocyte aneuploidy.
Conclusions:
FISH analysis of the first and second polar body in donor oocytes gave an aneuploidy rate of 19.1 %. This study shows the majority of errors occur during Meiosis I.
Related Concept Videos
Meiosis II
Meiosis II
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...
What is Meiosis?
Although meiosis shares similarities with mitosis—both rely on microtubules to...
What is Meiosis?
Oogenesis
Each primary oocyte is surrounded by a layer of pre-granulosa cells, forming what is known...
Oogenesis

