Question

Outline the events that occurred during the formation of gametes. Include the locations (be specific. Which cells undergo mitosis or meiosis? When does game information occur? For the female, take to process all the way to ovulation..

Answer 1

Female gamete formation:-

• OOGENESIS - It is a process taking place in female body to form mature female gametophyte.
• In this process, there are three phases - 1. Multiplication phase 2. Growth phase 3. Maturaion phase
• Primordial germ cells originating from the endoderm of yolk sac migrate to the gonad and get differentiated into the oogonia.
• They undergo a series of mitotic divisions , and get arranged as clusters - Multiplicaion phase
• certain oogonia instead of going to further multiplication, differentiate into primary oocyte.
• Before the birth, most of this oogonia degenerates.
• each primary oocyte gets surrounded by a single layer of squamous epithelium - known as primordial follicle.
• this primary oocyte enters into prophase (diplotene) of 1st meiotic divsion.
• at birth, all primary oocytes finished prophase of first meiotic division but instead of proceeding into the metaphase, they enter dictyotene sstage.
• They finish their meiotic division before puberty is reached.
• With the onset of puberty, a number of primordial follicles begin to mature with each ovarian cycle.
• Now the processes are under the influence of FSH and LH.
• The primary oocyte still is in dictyotene stage begins to increase in size, while surroounding cells change from flat to cuboidal. - now it is called primary follicle.
• inially follicular cells are in intimate contact with oocyte, but soon a layer of mucopolysaccharide is deposited on the surface of oocyte which is produced by follicular cells and the oocyte.this layer is defined as zona pellucida.
• later, these follicular cells proliferate, forming a thick cellular layer of granulosa cells around the oocyte.
• under influence of FSH, follicular antrum forms.
• the follicular cells surrounding the oocyte remain intact and form cumulus oophorus.
• In large teritary teritary follicles, the granulosa cells immediately surrounding the zona pellucida become columnar and radially disposed to form corona radiata, which provides nutrients to oocyte. Membrana granulosa is surrounded by theca interna and theca externa.
• When follicle matures, The primary oocyte undergo 2nd meiotic division.
• Thus forming two daughter cells - which are haploid , but unequal in size.
• the secondary oocyte receives all the cytoplasm, except the cytoplasm from the polar body
• just before ovulation, the first meiotic division takes place.
• The second meiotic division is completed only if oocyte is fertilized, otherwise it degenerates.

Male gamete Formation - Spermatogenesis:-

• in spermatogenesis, mature spermatozoa is formed from stem cells
• there are mainly two phases - spermatocytogenesis and spermiogenesis
• spermatocytogenesis - it is proliferative phase where spermatogonia cells undergoes mitotic division followed by meiotic division to produce haplloid gametes
• stem cells or spermatogonia are located in the basal compartment of seminiferous tubules
• the mitotic division of stem cells result in one cell being replacement for the cell that has just divided
• the other one become type A spermatogonia, which reachs adluminal compartment by migrating through sertoli cell barrier
• type A spermatogonia undergo further mitotic division to form type B spermatogonium
• this resulting type B spermatogonia undergoing the last mitotic division to form, diploid primary spermatocyte
• the primary spermatocyte undergo meiotic diviision to form secondary spermatocyte,, which again undergo meiotic division to form haploid spermatids
• spermiogenesis - this phase involve maturation of spermatids which is present in the adluminal compartment
• a series of nuclear and cytoplasmic changes occur and transformation from non motile to motile also occur
• thus formed mature spermatocyte is released into the lumen of seminiferous tubule as spermatozoa