GEN BIO 2 | Gametogenesis and Reproductive System

Mitosis

• primary involved in asexual reproduction and general cell growth and repair

• produces two identical diploid daughter cells that retain the number of parent cell chromosomes

• has one cell division

• occurs in somatic or body cells

• does not increase genetic variation

• does not form tetrads

Meiosis

• producing the gametes

• produces four unique haploid daughter cells that half the number of parent cell chromosomes

• has two cell divisions

• occurs in germ cells and reproductive cells

• increases genetic variation through crossing over and independent assortments

• forms tetrads in prophase I

Gametogenesis

the production of gametes or the sperm cells in males and the egg cells in females

Spermatogenesis

• produces sperm in seminiferous tubules

• reduces chromosome number from diploid to haploid

• continuous and prolific in adult males

• takes seven weeks

• all four products develop into mature gametes

Testes

produce sperm and male sex hormones

Epididymis

tightly coiled tube behind each testicle, where site of sperm maturation and some storage of sperm

Vas Deferens

conduct and store sperm

Seminiferous Tubules

highly coiled tubes that contains cells undergoing spermatogenesis, where sterm is produced

Spermatogonia

the diploid cells where spermatogenesis starts

Spermatogenesis Process

1. Spermatogonia undergo mitosis divide to produce primary spermatocytes.

2. The secondary spermatocytes move away from the outer wall, increase in size, and undergo meiosis I to produce secondary ones.

3. The secondary spermatocyte undergoes meiosis II to produce four spermatids.

4. Spermatids undergo the spermatogenesis to differentiate into sperm.

5. Sertoli cells support and nourish sperm cell.

Spermatozoa Head

contains a nucleus and covered by the acrosome cap with digestive enzymes

Acrosome

the cap located on the head of the spermatozoa with the enzymes for egg penetration

Middle Piece

contains mitochondria

Spermatozoa Tail

a flagella that lets sperm swim towards an egg

Oogenesis

• making of egg cell within ovaries

• prolonged process in female adults, where immature eggs in female embryo do not complete their development until years later.

• Cytokinesis is unequal as the cytoplasm all goes towards a single daughter cell. This ensure the egg has enough resources for the early stages of development.

• Only one daughter cell becomes the egg, as the other products degenerate.

Ovary

produces egg and the female sex hormones

Uterine Tubes

also known as the fallopian tubes, it is the pathway for egg and sperm cells for fertilization

Uterus

houses developing embryo and fetus

Vagina

organ of sexual intercourse, birth control

Cervix

narrow part of uterus that connects to the vagina

Oogonia

diploid germ cell that egg cell production begins with; produced from primordial germ cells

Follical Stimulating Hormone (FSH)

it periodically stimulates a small number of follicles to resume growth and development; only one follicle fully matures per month

Ovulation

the release of the secondary oocyte

Corpus Luteum

what the ruptured follicle turns into; it secretes estradiol and progesterone

Progesterone

a hormone that helps maintain the uterine lining during pregnancy

Polar Bodies

the other smaller products of oogenesis that degenerate

Ovum

the mature egg cell

Oogenesis Process

1. The oogonia divides by mitosis and differentiate to to form diploid primary oocytes.

2. The primary oocytes begin meiosis but stop the process at prophase I before birth.

3. The primary oocytes reside within a small follicle, a cavity lined with protective cells.

4. At birth, both ovaries contain 1-2 million primary oocytes but only 500 fully mature between puberty and menopause.

5. Beginning at puberty, primary oocytes undergo meiosis I and divides into a small polar body and larger secondary oocyte.

6. The secondary oocyte begins meiosis II but stops at metaphase.

7. The follicle cells burst, releasing the secondary oocyte in ovulation as it enters the uterine tube.

8. The ruptured follicle becomes a corpus luteum.

9. If the oocyte is not fertilized, the corpus luteum degenerates as a new follicle matures during the next cycle.

10. If a sperm fertilizes it, the secondary oocyte completes meiosis II.

11. The secondary oocyte divides unequally to produce a polar body and the ovum.

Luteinizing Hormone (LH)

triggers gametogenesis in ovaries or testes

Tropic Hormones

regulate the activity of endocrine cells and glands

Gonadotropins

hormones that act on male and female gonads that allow them to produce the needed sex hormones

Gonadotropin-releasing Hormones (GnRH)

These hormones from the hypothalamus stimulates the anterior pituitary gland to release FSH and LH. It triggers the release of androgens in the form testosterone and the release of estrogen which is principally estradiol and progesterone.