MCQsOnline - Online Collection of MCQs of Medical PG Entrance Exams.

MCQ stands for Multiple Choice Questions sometimes called as Objective type questions. Here we discuss the Old Question Papers, High Yield Points and Strategies with respect to the Indian Medical Post Graduate PG Entrance Exams like AIIMS,AIPG, JIPMER, CMC Vellore, PGI Chandigarh, UPSC, TNPSC, State PG Exams like Tamil Nadu PG (TN PG), Delhi PG, UPPG, Tamilnadu PG (TNPG), Karnataka PG, MAHE, COMED-K etc.

Target PG

PG Preparation

Related Portals

Search This Site

If you cannot locate what you want to find, please search using the box given below

Sunday, January 06, 2008

Polar bodies are formed during Oogenesis

010. Polar bodies are formed during :

1. Spermatogenesis.

2. Organogenesis.

3. Oogenesis.

4. Morphogenesis.

Answer

3. Oogenesis.

Reference

Gray 38th Edition Page 123

Quality

Spotter

Status

Repeat

QTDF
All books

Discussion

The poles of the spindle in oöcytes lack centrioles and are composed of pericentriolar material. As anaphase approaches, the homologous pairs of chromosomes move towards the poles of the spindle. A bulge forms at the site of the spindle which is destined to become the first polar body. The midbody forms around the spindle and initiates cleavage of the first polar body and final separation of the homologous chromosomes occurs. Unlike the equal division of the nucleus, the division of the cytoplasm is highly unequal, the polar body carrying with it its numerically equal chromosomal complement and an exiguous share of the cytoplasm. (The first polar body is occasionally seen to cleave into two equal fragments before degenerating sometime after ovulation.)

Comments

The oöcyte resulting from this reduction division is known as the secondary oöcyte; it contains 23 double-stranded chromosomes. In the absence of an interphase the chromosomes are rearranged around the equator of a second spindle. At metaphase of the second meiotic division the secondary oöcyte arrests until fertilization or parthenogenetic activation stimulates the completion of meiosis which is marked by extrusion of the second polar body.

Tips

Accumulation of lecithin like substance the deutoplasm within the cytoplasm of oocytes makes the nucleus eccentric in position. This explains why in female, the primary oocyte gives rise to a single mature ovum with the extrusion of first and second inactive polar bodies in the process of maturation of female gametes. But in similar process of maturation of male gametes, one primary spermatocyte gives rise to four active spermatids because nucleus of the primitive male sex cells is central in position.

No comments:

Post a Comment