first polar body

The first division results in a small "first polar body" and a much larger daughter cell.

The first polar body formed is usually larger than the second one, and often divides into two after its separation from the ovum.

Therefore the formation of the first polar body is an especially important factor in forming a healthy zygote (3).

(Frequently the first polar body degenerates in many strains of mice.)

As a result of meiosis I, the primary oocyte has now developed into the secondary oocyte and the first polar body.

Since the first polar body normally disintegrates rather than dividing again, meiosis in female mammals results in three products, the oocyte and two polar bodies.

For example, predivision, the separation of chromatids before anaphase, in the first polar body can induce the formation of an aneuploid polar body.

The M I plate or the first polar body and M II plate were removed by aspiration with a 15-μm inner diameter glass pipette.

By this time, the oocyte has completed meiosis I, yielding two cells: the larger secondary oocyte that contains all of the cytoplasmic material and a smaller, inactive first polar body.

As mentioned earlier, chromosomal abnormality in the first polar body can result in a healthy embryo, meaning that eggs may in fact be wasted as a result of the screening.

By screening the first polar body for chromosomal anomalies, non-viable eggs can be reliably identified, though eggs with normal first polar bodies can still be affected by errors.

When the majority of errors occur in chromatids rather than entire chromosomes (a condition correlated with the age of the mother), screening only the first polar body will fail to detect a large percentage of defective eggs.

The first and second polar body of the oocyte are extruded at the time of the conclusion of the meiotic division, normally the first polar body is noted after ovulation, and the second polar body after fertilization.

Errors can occur during either of the two meiotic divisions that produce each polar body but are more pronounced if they occur during the formation of the first polar body because the formation of the first polar body influences the second.