Animal Reproduction and Development Flashcards

Sexual and Asexual Reproduction

  • Sexual Reproduction: Fusion of sperm and ovum, leading to varied genotypes.
  • Asexual Reproduction: Single parent reproduction, offspring are clones. Common in invertebrates.
    • Forms include budding, regeneration, and parthenogenesis.
  • Advantages/Disadvantages:
    • Asexual: Rapid reproduction, prevalent in stable environments.
    • Sexual: Genetic variation.

Gametogenesis

  • Production of gametes in gonads (testes/ovaries).
  • Germ cells multiply via mitosis into spermatogonia/oogonia (2n).
  • These undergo mitosis and then meiosis I & II to form haploid gametes.

Spermatogenesis

  • Spermatogonium (2n) → primary spermatocyte (2n) → 2 secondary spermatocytes (n) → 4 spermatids → sperm.
  • One cell yields four gametes.
  • Sperm Anatomy:
    • Head: Acrosome (enzymes for egg penetration).
    • Midpiece: Mitochondria (energy).
    • Tail: Flagellum.

Oogenesis

  • Oogonium (2n) → primary oocyte (2n) → polar body + secondary oocyte (n) → second polar body + haploid egg.
  • One gamete per primary oocyte.
  • Process begins in embryo, stalls at meiosis I until puberty.
  • Meiosis II completes upon fertilization.

Gametogenesis Comparison

  • Spermatogenesis: All 4 products become sperm, occurs throughout adolescence/adulthood, continuous production.
  • Oogenesis: One product becomes egg, mitotic divisions end before birth, production stops around age 50, prolonged interruptions.

Follicle and Oocyte

  • Cumulus mass protects and nourishes the oocyte.
  • Theca produces hormones for oocyte growth.
  • Zona pellucida surrounds the secondary oocyte.

Fertilization

  • Haploid egg + sperm = diploid zygote.
  • Sperm uses species-specific attractants.
  • Acrosomal Reaction: Enzymes digest zona pellucida.
  • Cortical Reaction: Blocks other sperm after fusion.

Fertilization Types

  • External: Aquatic environments.
  • Internal: Within female reproductive tract.

Male Anatomy

  • External: Scrotum, penis.
  • Internal: Testes (sperm, hormones), accessory glands, ducts.
  • Scrotum maintains testes temperature.
  • Seminiferous tubules: Spermatogenesis.
  • Leydig cells: Testosterone.
  • Sertoli cells: Nourish sperm.

Semen

  • Sperm + secretions from seminal vesicles (fructose), prostate gland (alkaline fluid), and bulbourethral glands (mucus).

Female Anatomy

  • External: Clitoris, labia.
  • Internal: Vagina, cervix, uterus, oviduct, ovaries.
  • Oocytes develop in ovaries, released into oviduct.
  • Fertilization in oviduct.
  • Zygote develops into blastocyst.

Oogenesis Cycle

  • Finite number of primary oocytes at birth.
  • Ovarian cycle ~28 days.
  • Menopause: Oocytes depleted.

Hormonal Control

  • Hypothalamus: GnRH (Gonadotropin-releasing hormone).
  • Anterior Pituitary: FSH (follicle stimulating hormone), LH (luteinizing hormone).
  • Gonads: Testosterone, estradiol, progesterone.

Male HPG Axis

  • GnRH → LH (Leydig cells: testosterone) & FSH (Sertoli cells: nourish sperm).
  • Testosterone: Spermatogenesis, secondary sexual traits.
  • Feedback: Testosterone inhibits GnRH and LH.

Female HPG Axis

  • GnRH → LH & FSH (follicle maturation) → Estrogen & Progesterone (uterus lining).

Follicular Phase

  • Follicle growth, estradiol increases.
  • Estradiol initially inhibits LH/FSH, then triggers LH spike for ovulation.

Ovulation

  • Follicle ruptures, releases egg.
  • Empty follicle becomes corpus luteum (progesterone).

Luteal Phase

  • Corpus luteum secretes progesterone, inhibiting FSH/LH.
  • If fertilization occurs, chorionic gonadotropin maintains corpus luteum.
  • If no fertilization, corpus luteum degenerates.

Uterine Cycle

  • Menstruation: Corpus luteum degenerates.
  • Proliferative Phase: Endometrium thickens.
  • Secretory Phase: Glands secrete nutrients.
  • If no implantation, lining sheds; if implantation, pregnancy begins.