Chap. 9 : Reproduction in Animal

• Asexual reproduction


  The genetic materials all come from one parent, without the fusion of egg and sperm. Offspring that are genetically identical to the parent.
• Sexual reproduction


  The genetic material of two individuals is combined to produce genetically diverse offspring that differ from their parents.
• Modes of asexual reproduction

  • Fission
  • Budding
  • Gemmules
  • Fragmentation and regeneration
  • Alternation of asexual and sexual reproductions
  • Parthenogenesis
  • Sequential hermaphroditism
  • Hermaphroditism
• Binary fission


  1. Separation of a parent cell into two or more daughter cells of approximately equal in size

  2. Separation of a parent's nucleus into half and once

  3. Produces two individuals that are identical and approximately equal in size
• Multiple fission


  Nucleus of a parent cell divides repeatedly and produces many individuals simultaneously
• Budding


  An outgrowth (bud) pushes out from the parent's cell, pinches off, and then enlarges into a new cell
• Gemmules


  Internal buds found in sponges and are involved in asexual reproduction. It is an asexually reproduced mass of cells, that is capable of developing into a new organism, for example, an adult sponge.
• Fragmentation and regeneration


  The breaking of the body into several pieces, some or all of which develop into complete adults. Fragmentation must be accompanied by regeneration, the regrowth of lost body parts.
• Sexual reproduction


  The creation of offspring by the fusion of male and female gametes to form a zygote. The female gamete is the egg. The male gamete is the sperm.
• Advantages of asexual reproduction

  • Even a single individual can reproduce
  • Many offsprings can be produced rapidly
• Disadvantages of asexual reproduction


  • May result in little or no genetic variation
• Advantages of sexual reproduction

  • Increase genetic variation among the offsprings
  • Enhances reproductive success in changing environments
• Disadvantages of sexual reproduction

  • Problem in locating a mate
• Reproductive cycles and patterns

  Most animals exhibit cycles in reproductive activity, often related to changing seasons. They are controlled by hormones and environmental cues (Example: changes in day length, seasonal temperature, rainfall, etc.)
• Hermaphroditism


  Each individual has both male and female reproductive systems, so any two individuals can mate
• Sequential hermaphroditism


  An individual reverses its sex during its lifetime
• Parthenogenesis


  A process in which an egg develops without being fertilized, resulting in a clone of the mother
• Comparison of sexual and asexual reproduction


  • Parent
  • Gamete
  • Meiosis
  • Progeny
• Internal fertilization


  The fusion of gametes (egg and sperm) inside of the body of a parent. Terrestrial animals typically use this method to prevent exposure and desiccation of gametes or embryos.
• External fertilization


  The fusion of gametes (egg and sperm) outside of the body of a parent. It is most common in aquatic animals, where the water acts as a medium via which the gametes can travel.
• Fertilization


  The union of egg and sperm. The main function is to bring the haploid nuclei of sperm and egg together to form a diploid zygote. Contact of the sperm with the egg's surface initiates metabolic reactions within the egg that trigger the onset of embryonic development.
• Pheromones


  Chemicals released by one organism that can influence the physiology and behavior of other individuals of the same species. They are small, volatile/water-soluble molecules that disperse into the environment and are active in tiny amounts. They function as mate attractants.
• All species produce more offspring than the environment can handle, but the proportion that survives is quite small
• Internal fertilization provides greater protection for the embryos of many terrestrial animals
• Many animals retain the embryo, which develops inside the female's reproductive tract, instead of secreting a shell around the embryo
• Parental care


  Many different types of animals exhibit parental care to ensure survival of offspring
• Modes of animal development

  • Oviparity
  • Ovoviviparity
  • Viviparity
• Oviparity


  Expulsion of undeveloped eggs rather than live young. The eggs may have been fertilized internally before released as used by many birds and reptiles.
• Ovoviviparity


  The young grow in eggs inside the mother's body and the mother gives birth to live young. Internal fertilization, no placental connection, the unborn young are nourished by egg yolk.
• Viviparity


  Development of the embryo inside the body of mother eventually leading to live birth. Internal fertilization, the growing embryo derives continuous nourishment from the mother usually though a placenta. Mostly in mammals.