The mother germ cells are transformed into a mature follicle through series of steps. Provide the missing steps in the blank boxes.
The germinal epithelial cells divide repeatedly until many diploid oogonia are formed. The oogonia grow to form primary oocytes. Each primary oocyte then gets surrounded by a layer of granulosa cells and then called the primary follicle. The primary follicles get surrounded by more layers of granulosa cells and called secondary follicles.
The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum. The primary oocyte within the tertiary follicle undergoes meiotic division to become a secondary oocyte and a first polar body (haploid).
The tertiary follicle further changes into the mature follicle or Graafian follicle. The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation.During reproduction, the chromosome number (2n) reduces to half ( $n$ ) in the gametes and again the original number ( $2 n$ ) is restored in the offspring. What are the processes through which these events take place?
The meiotic cell division reducers the chromosome numbers to half during gametogenesis and diploid (2n) number of chromosome is restored by the union of male and female gamete through process of fertilisation.
What is the difference between a primary oocyte and a secondary oocyte?
Primary oocyte is a diploid cell formed in foetal ovary when the gamete mother cell, oogonia is arrested at prophase-l of meiosis. Secondary oocyte is the haploid cell formed from primary oocyte that completes its first meiotic division, during puberty and produces the female gamete ova(n).
What is the significance of ampullary-isthmic junction in the female reproductive tract?
The act of fertilisation takes place in the female genital track that is at the junction of the isthmus and ampulla (ampullary - isthmic junction) of the Fallopian tube.
How does zona pellucida of ovum help in preventing polyspermy?
When a sperm penetrates ovum, it induces changes in the membrane that make the zona pellucida layer impenetrable to additional sperms. Thus, it ensures that only one sperm can fertilise an ovum and stops polyspermy.