Question

In a six year old girl, the oogenetic cell she has is ____(i)____ and it is in _____(ii)_____ phase of the cell cycle.

Choose the correct option

• A. (i)- primary oocyte, (ii)- prophase-I
• B. (i)- secondary oocyte, (ii)-prophase-I
• C. (i)- primary oocyte, (ii)- metaphase -II
• D. (i)- secondary oocyte, (ii)- metaphase-II

Answer 1

The correct option is A (i)- primary oocyte, (ii)- prophase-I

The process of formation of a mature female gamete is called oogenesis.
In human female, this process is discontinuous and occurs at different stages of life.
The cells of the germinal epithelium of the ovary divide by mitosis producing undifferentiated germ cells called oogonia in the ovary of the foetus.
Oogonia multiplies by mitotic divisions and grows into primary oocytes. Meiosis begins in the primary oocytes soon after their formation. But it gets arrested in the first stage of prophase-I.

At the time of birth, all the future eggs are in the prophase stage.The process of oogenesis is paused until the girl child attains puberty.

At adolescence,(i.e after 10-13 years ) anterior pituitary hormones cause the development of a number of follicles in an ovary, this results in the primary oocyte finishing the first meiotic division. Each primary oocyte gets surrounded by layers of granulosa cells forming primary, secondary and tertiary follicles. At this stage, the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body. This secondary oocyte commences meiosis- II and gets arrested in metaphase-II, which is completed only if it gets penetrated by a sperm.

In the given question, the girl child is four years old. Generally puberty is attained around the age of 11. Thus in this case the oogenetic cell she has is primary oocyte and it is arrested in the prophase-I of the cell cycle.