Question

The second maturation division of the mammalian ovum occurs

• A. Until after the ovum has been penetrated by a sperm
• B. Shortly after ovulation before the ovum makes entry into the Fallopian tube
• C. In the Graafian follicle following the first maturation division
• D. Until the nucleus of the sperm has fused with that of the ovum

Answer 1

The correct option is A

Until after the ovum has been penetrated by a sperm

The correct option is A

Explanation of the correct option:

1. The second maturational division (meiosis II) of the secondary oocyte continues, however it is stopped at the metaphase stage.
2. The ovum is shed during ovulation while the oocyte is in this stage.
3. It enters the oviduct, where the cell cycle doesn't start again until the sperm arrive.
4. Oogenesis is the process by which female gametes are created.
5. In contrast, in placental mammals, the egg ceases to be referred to be an egg once it has been fully formed and fertilized and has started to divide.

Explanation of the incorrect option:
Option B:

After the sperm enters, the second meiotic division in the secondary oocyte is finished.

Option C:

1. The primary oocyte undergoes its first maturation division, which results in the formation of a secondary oocyte and a first polar body.
2. In the secondary oocyte, the second maturation division quickly takes place.
3. In this division, the nucleus is split into a mature egg nucleus and a second polar body nucleus without being followed by cytoplasmic fission.

Option D:

1. The DNA in the sperm nucleus has a distinctive chromatin structure that is severely compressed and linked to certain proteins called protamines.
2. It is a transcriptionally dormant cell that is not dividing.
3. Sperm and ovum fusing as fertilization.
4. The haploid nucleus of sperm fuses with that of the ovum to form the diploid zygote.

Final answer: The second maturation division of the mammalian ovum occurs after the ovum has been penetrated by a sperm.