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.