Unit 6.6 and 11.4 - Sexual reproduction

Question 1

What are the 6 different stages of sperm cells (in order of production)

Answer 1

• Germinal epithelial cell
• Spermatogonia
• Primary spermatocyte
• Secondary spermatocyte
• Spermatid
• Spermatozoa

Question 2

What cell is responsible for spermatid differentiation into spermatozoa?

Answer 2

Sertoli cell

Question 3

Where does spermatozoa production occur

Answer 3

In the seminiferous tubule

Question 4

Explain how spermatozoa is produced

Answer 4

Produced in the testes (seminiferous tubules). Germinal epithelial cells in the seminiferous tubules undergo mitosis to form spermatogonia (2n), this then undergoes mitosis again to form primary spermatocytes (2n), this then undergoes meiosis I to form secondary spermatocytes (n), this then undergoes meiosis II to from spermatids (n), these cells then differentiate with the aid of the Sertoli cells which nourish the spermatids (n), this forms spermatozoa (n).

Question 5

Explain how an ovum is produced

Answer 5

Produced in the ovaries. Germinal epithelial cells (2n) undergo mitosis to form oogonium (2n), this then undergoes mitosis into a primary oocyte (2n) - this occurs as an embryo, prior to birth - and a polar body (which degenerates). This then undergoes meiosis I (stuck in prophase I) to become a secondary oocyte (n) in puberty. Secondary oocyte (stuck in prophase I) then undergoes meiosis II when fertilised to become an ovum.

Question 6

Compare and contrast oogenesis and spermatogenesis

Answer 6

Similarities:
- Produces genetically varied gamete(s)
- Undergoes mitosis and meiosis

Differences:
- Starts in puberty (spermatogenesis), starts before birth (oogenesis)
- No pauses in spermatogenesis, pauses in oogenesis
- Spermatozoa production doesn’t cease, ovum production ceases eventually (menopause)
- Produces 1 ovum, produces 8 sperm (per spermatogonia)
- Released on ejaculation (spermatozoa), released by ovulation (oogenesis)

Question 7

How is sex defined biologically speaking?

Answer 7

Humans contain 46 chromosomes, and 2 of them contain SDR (sex determining regions) and this SDR determines what gonads will be developed. If XY chromosome (Y chromosome contains TDF, testis determining factor) then male, if XX (no TDF) then female.

Question 8

How does In Vitro Fertlisation work?

Answer 8

Three main steps:

Down regulation:
- Regular menstrual cycle is stopped through hormone blockers to ensure no follicles or stimulated or ovulation occurs

Super ovulation
- after 2 weeks the patient is given high amounts of FSH to promote multiple eggs’ ovulation, this is then extracted for external fertilisation

Fertilisation
- male sperm sample is injected with healthy sperms (no polyspermy i.e.) in order for the embryo to develop

Implantation
- this zygote is then implanted in the endometrium and the patient is given progesterone to ensure the lining is thick enough for the implantation and development of the embryo