Animal reproduction
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Animal Reproduction. Two Modes. Asexual – Invertebrates Fission Splitting into two Budding Splitting off parent Sponges produce gemmules Fragmentation Parent breaks into pieces Mature individuals are created through regeneration. Arm of a star fish create an adult. Sexual

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Animal Reproduction

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Animal Reproduction


Two Modes

  • Asexual – Invertebrates

    • Fission

      • Splitting into two

    • Budding

      • Splitting off parent

        • Sponges produce gemmules

    • Fragmentation

      • Parent breaks into pieces

      • Mature individuals are created through regeneration.

        • Arm of a star fish create an adult.

  • Sexual

    • Involve a large non-motile cell

      • Ovum

    • Small Mobile Cell

      • Spermatazoan


Advantages and Disadvantages of Asexual Reproduction

  • Advantages

    • Enables the animal to reproduce in an isolated environment.

    • Many offspring can produced very quickly and thus colonize a new habitat rapidly

    • Ideal for stable environments

  • Disadvantages

    • No genetic variability in case the environment changes

    • One disease can kill the entire population


Reproductive Patterns Vary

  • Some animals will switch to sexual reproduction under environmental stress and reproduce asexually under favorable conditions.

  • Some animals only reproduce through parthenogenesis.

    • Adult develops from an unfertilized egg

    • Adults that develop in this manner are usually haploid

      • Whip tail lizards create a diploid zygote by doubling their chromosomes after meiosis

      • There are no males

      • Mating females switch roles and act male or female depending on the level of estrogen or progesterone in their bodies.


Sexual Reproduction is a Problem for Sessile, Burrowing or Parasitic animals.

  • Solution?

    • Hemaphroditism

      • Have both male and female reproductive organs.

    • Sequential Hemaphroditism

      • Species switch sexes during their lifetime.

        • Protogynous - female first

        • Protandrous - male first

        • Reef fish call wrasses switch from female to male based on size


Spermatogenesis


The Sperm


Oogenesis


Menstral CyclePreparing the Endometrium

  • There are three phases

    • Proliferative - endometrium thickens

    • Secretory – endometrium becomes vascular and creates glandular structures.

    • Menstral flow – endometrium is expelled.


Ovarian CyclePreparing the Egg

  • There are three phases

  • Follicular – several follicles begin to grow

    • Ovulation – one follicle matures and breaks out of the ovary

    • Luteal phase – remaining follicular tissue becomes glandular.

      • Secretes estrogen and progesterone to support the growing endometrim.


There are Five Hormones that Synchronize the ovarian and Menstral Cycles

  • GnRH, FSH, LH, Estrogen, and Progesterone

  • GnRH

    • Gonadotropin releasing hormone

    • Released by the hypothalamus

    • Causes the pituitary to releases FSH and LH

  • FSH

    • Follicle stimulating hormone

    • Respond to receptors on the follicle and encourage growth

    • Growing follicles secrete estrogen

    • Small amounts of estrogen inhibit the release of FSH and LH from the pituitary.

    • A steep rise in the release of estrogen from the follicle cause the opposite effect and stimulate the release of FSH and LH from the pituitary.

    • The follicle now respond to receptors for LH.


  • LH

    • Lutenizing Hormone

    • Cause the maturation of the follicle and it is released from the ovary

    • The follicular tissue left behind now becomes the corpus luteum which is glandular in function and secretes estrogen and progesterone.

  • Estrogen and Progesterone

    • An increase in the production of these hormones inhibit the hypothalamus and pituitary which inhibits the release of FSH and LH.

    • Progesterone supports the endometrium

    • Without LH the corpus luteum disintegrates

    • Without progesterone the endometrium disintegrates.

      • Blood vessels are choked off and the uterus undergoes spasms.

      • The endometrium is expelled

    • Without the corpus luteum the hypothalamus and pituitary can once again release FSH and LH and the follicular phases begins again.


Zygote Formation


Placental Circulation


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