Chapter 46: Animal Reproduction

Types of Reproduction

Asexual Reproduction

• Offspring formed without fusion of eggs and sperm.
• Genes come from one individual; recombination possible.
• Mechanisms:
  • Fission: Parent splits into two/more individuals.
  • Budding: New individuals arise from outgrowths of existing ones.
  • Fragmentation: Body breaks into pieces, some/all develop into adults, requiring regeneration.
  • Parthenogenesis: New individual from an unfertilized egg.
• Advantages:
  • Useful for sessile animals or those in low-population areas.
  • Produces many offspring; beneficial in stable environments.

Sexual Reproduction

• Offspring formed by fusion of male gamete (sperm) and female gamete (egg) forming a zygote.
• Pros:
  • Genetic variation.
  • Increased reproductive success in varied environments.
  • Can help eliminate deleterious genes over time.
• Cons:
  • Sexual females produce fewer daughters compared to asexual females.

Reproductive Strategies

Reproductive Cycles

• Related to seasons; influenced by hormones and environmental cues.
• Climate change impacts reproductive success.
• Ovulation: Release of mature eggs; midpoint of female cycle.
• Some animals reproduce both sexually and asexually.

Hermaphroditism

• Individuals with both male and female reproductive systems.
• Allows self-fertilization or mating with any individual.

Fertilization

• External Fertilization: Eggs shed and fertilized externally.
• Internal Fertilization: Sperm deposited near female reproductive tract; leads to higher survival rate.
• Timing critical for successful fertilization.

Parental Care

• Internal fertilization leads to fewer gametes but higher survival rates due to enhanced protection.
• Parental care, especially after birth, ensures offspring survival.

Reproduction Partners and Structures

Human Reproductive System

• Female Structures:
  • External: Clitoris, labia.
  • Internal: Ovaries, uterus, fallopian tubes.
• Male Structures:
  • External: Scrotum, penis.
  • Internal: Testes, ducts.

Gamete Production

• Spermatogenesis: Continuous process; produces millions of sperm daily.
• Oogenesis: Eggs develop over years.

Hormonal Regulation

Female Cycles

• Coordinated by hormones via hypothalamus, pituitary, and gonads.
• Menstrual Cycle: Prepares endometrium for potential implantation.
• Ovarian Cycle: Follicular growth and ovulation.

Male Hormonal Control

• FSH and LH: Promote Sertoli cells and Leydig cells for sperm production.

Pregnancy and Childbirth

Fertilization to Birth

• Fertilization in oviduct; zygote undergoes cleavage.
• Implantation: Blastocyst implants in endometrium.
• Gestation: Typically three trimesters.
• Parturition (Labor): Dilation, expulsion, and placental delivery.

Contraception Methods

• Prevents pregnancy via various methods (e.g., barriers, IUDs, birth control pills).

Challenges and Technology

Reproductive Issues

• Infertility: Addressed through techniques like in vitro fertilization (IVF).
• Genetic Testing: Amniocentesis, sonograms, and ethical considerations.

These notes provide a summary of the key points from the presentation on animal reproduction, covering both asexual and sexual reproduction, human reproductive systems, hormonal regulation, fertilization, and modern reproductive technologies.