Monday, March 29, 2010

[Biology Form 5] Meeting Gametes

Study the following details for a better understanding of gametogenesis and what happens after it.
  1. Process and location
    • Male - Spermatogenesis in the testes.
    • Female - Oogenesis in the ovaries.

  2. Parent cell for gametogenesis
    • Male - Primary spermatocyte.
    • Female - Primary oocyte.

  3. Cell produced after Meiosis I
    • Male - Two secondary spermatocytes.
    • Female - One secondary oocyte (X) and one (1st) polar body (Y).

  4. Cell produced after Meiosis II
    • Male - Four spermatids.
    • Female -
      • From the secondary oocyte (X): One ovum + One polar body.
      • From the first polar body (Y): Two other polar bodies.

  5. What happens to cells produced after Meiosis II?
    • Male - Spermatids differentiate into sperms.
    • Female - All three polar bodies will degenerate; only the ovum will survive.

  6. When does Meiosis II occur?
    • Male - Immediately after Meiosis I.
    • Female -
      • For the first polar body: immediately after Meiosis I.
      • For the second oocyte: only after a sperm penetrates the oocyte.

  7. What happens during sexual intercourse?
    • Male - Sperms are ejaculated from a male's penis into a female's vagina.
    • Female - Sperm from a male swim upwards, from a female's vagina, through the cervix, into the uterus and then to the Fallopian tubes.

  8. Site for fertilisation
    • Male - none.
    • Female - In the Fallopian tubes of the female reproductive system.

  9. Product of fertilisation
    • Male - none.
    • Female - A diploid zygote (containing 46 chromosomes), which then develops into an embryo.

What happens after sexual intercourse?
  • Possibility I
    • A sperm meets the secondary oocyte and penetrates it.
    • Meiosis II quickly occurs in the secondary oocyte, and an ovum and a polar body is formed.
    • The polar body degenerates.
    • The nucleus of the ovum fuses with the nucleus of the sperm.
    • Fertilisation is successful and a diploid zygote is formed.
    • The female is pregnant.

  • Possibility II
    • None of the sperms meet the secondary oocyte. This could mean ovulation has
      • not occurred yet;
      • occurred but the secondary oocyte, which can only live for 24 hours, has died.

    • No fertilisation occurs.
    • No zygote is formed.
    • The female is not pregnant; she gets her next period as usual.

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