Question 3

Question 1

Describe the process of oogenesis

Answer 1

In the prenatal phase, a 2N primordial germ cell undergoes mitosis and produces oogonia. Mitosis continues and produces primary oocytes (still 2N). Meiotic prophase of primary oocytes begins, Oogenesis undergoes nuclear arrest during meiotic prophase 1 of primary oocytes. These primary oocytes are stored in the ovaries as primordial follicles until recruitment. Primordial follicles are then recruited by FSH. They begin to form primary follicles. The follicles with more FSH receptors make it to the selection phase. LH begins to take over follicular development, and only the few largest follicles with the most LH receptors grow into tertiary follicles. In the dominance phase, only the largest follicle remains (dominant pre-ovulatory follicle). LH continues to act on the dominant follicle until it ovulates.
After ovulation, high levels of LH end nuclear arrest. The primary oocyte will then finish meiosis one, becoming a secondary oocytey. After fertilization, the secondary oocyte completes meiosis 2, allowing a zygote to form.

Question 2

Describe the process of spermatogenesis

Answer 2

Spermatogenesis occurs in the seminiferous tubules in the parenchyma continuously after the animal hits puberty. Male is provided with a continual supply of gametes, billions of sperm per day. Three phases of spermatogenesis are: proliferation, meiosis and differentiation. In proliferation, spermatogonia undergo mitotic division from spermatogonia A1 -> A2 -> A3 -> A4. They can then continue mitotic division into either spermatogonia (I) then (B) (which then mitotically divide and return to A1 spermatogonia for constant replacement of spermatogonia) or they divide into primary spermatocytes. During meiosis, primary spermatocytes go through meiosis 1 to produce secondary spermatocytes, which undergo meiosis 2 to produce haploid spermatids. During differentiation (spermogenesis), spermatids develop into fully formed spermatozoa.
The seminiferous lumen is divided into two compartments (basal and adluminal) through junctional complexes. This is part of the blood-testis barrier which prevents the male immune system from affecting the developing sperm. Proliferation occurs in the basal compartment, while meiosis and differentiation occur in the adluminal compartment.
There are four phases in differentiation: golgi, cap, acrosomal and maturation. They turn a round spermatid into a functional spermatozoa with a distinct head, neck, middle piece and principal piece.

Question 3

Memorize diagrams

Answer 3

OK

Question 4

Describe the phases of differentiation

Answer 4

1. Golgi phase: acrosomic vesicle formation and centriole migration
2. Cap phase: acrosomic vesicle spreads over nucleus and initiation of axoneme (tail) formation
3. Acrosomal phase: nuclear + cytoplasmic elongation & neck +annulus formation
4. Maturation phase: final assembly of sperm