Sexual Reproduction in Mammals

Introduction to Reproduction

Reproduction: The biological process by which new individual organisms are produced.

• Essential for the survival and continuity of species over generations.
• Prevents species from becoming extinct.

General Concept of Reproduction in Biology

• Sexual Reproduction:
  • Requires two parents and involves the mixing of genetic material.
  • Promotes genetic diversity.
  • Examples: Humans, lions, elephants.
• Asexual Reproduction:
  • Involves a single parent, producing genetically identical offspring.
  • Enables rapid population growth.
  • Examples: Bacteria, certain plants.

Connection between Heredity and Reproduction

• Role of Reproduction in Heredity:

  • Transfers genetic information from parents to offspring.

• Genes:

  • Units of heredity conveying traits, essential for evolution.
  • Related to Darwin's "survival of the fittest" — advantageous traits.

• Hereditary Traits in Mammals:

  • Fur colour and eye shape.
  • Aid in survival through camouflage with their surroundings.

Hormonal Regulation in Mammals

Hormones are central to reproductive success, ensuring the coordination of complex processes such as ovulation and gestation. For example, during the oestrous cycle, oestrogen and progesterone regulate ovulation and prepare the uterine environment for potential pregnancy.

Key Reproductive Hormones

• Testosterone: Primary hormone in males.
  • Produced in the testes.
  • Supports sperm production and development of secondary sexual characteristics.

Hormonal Regulation of Reproductive Cycles

Female Mammals

• Oestrous Cycle: Phases include proestrus, oestrus, metoestrus, and dioestrus.
  • Proestrus: Oestrogen levels increase, and follicles develop.
  • Oestrus: Peak oestrogen triggers ovulation, facilitating fertilisation.
  • Metoestrus: Progesterone rises, preparing for embryo implantation.
  • Dioestrus: If pregnancy does not occur, progesterone declines, and the cycle restarts.

Male Mammals

• Sperm Production Regulation:
  • Testosterone initiates sperm creation, maintained by feedback mechanisms.

Introduction to Sexual Reproduction Processes

Sexual reproduction in mammals is an essential biological process where two parents contribute genetic material to produce offspring. This process promotes genetic diversity, which is crucial for species adaptation and survival. Consider genetic recombination like shuffling a deck of cards, where each shuffle results in a unique hand, promoting variation.

Reproductive System Components

Male Reproductive System

• Testes: Produce sperm and hormones necessary for reproduction.
• Vas deferens: Transports sperm from the testes to the prostate.
• Prostate: Produces seminal fluid to nourish and protect sperm.
• Penis: Facilitates the transfer of sperm into the female reproductive system.

Female Reproductive System

• Ovaries: Produce eggs and hormones.
• Fallopian Tubes: Transport eggs from the ovaries to the uterus.
• Uterus: Site for housing and nurturing the fertilised egg.
• Cervix: Serves as a gateway between the uterus and vagina.
• Vagina: Receives sperm during mating.

Gamete Roles

• Male Gametes (Sperm): Formed through meiosis in the testes, essential for fertilisation.
• Female Gametes (Eggs): Also formed through meiosis in the ovaries.
• Meiosis reduces chromosome numbers and introduces genetic variation.

Fertilisation and Zygote Formation

• Fertilisation occurs when sperm and egg meet, combining genetic material to form a zygote.
• Zygote Formation marks the start of a new life, leading to development progressing to a foetus.

Internal Fertilisation

Comparison with External Fertilisation

• Environmental Control: Internal fertilisation allows consistent, controlled conditions.

Advantages of Internal Fertilisation

• Protection of Gametes: Shields sperm and eggs from predators.
• High Success Rate: Increased fertilisation chances due to proximity.
• Embryo Care: Provides continuous nourishment, enhancing survival prospects.

Advantages of Sexual Reproduction

Sexual reproduction offers notable advantages over asexual reproduction by introducing genetic variation.

• Recombination: Exchange of genes to foster diversity.
• Independent Assortment: Random distribution of chromosomes resulting in new combinations.

Evolutionary Benefits

• Sexual reproduction leads to diverse phenotypes, facilitating adaptation.

Heredity and Genetic Variation

• Heredity: The transmission of genetic traits to offspring.

Environmental and Social Influences

• Environmental and Social Factors: Affect mammal reproduction, such as bears timing cub births to ensure food availability.

• Temperature:

  • Changes signal breeding times.

• Social Factors:

  • Mating systems affect reproductive success.