lase

• Sexual reproduction


  A type of reproduction in which the genetic materials from two different cells combine, producing an offspring
• Sex cells


  The cells that combine in sexual reproduction
• Fertilization


  1. Egg cell and sperm cell join together

  2. A new cell called a zygote is formed

  
• Meiosis


  1. A type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes (the sex cells, or egg and sperm)

  2. In humans, body (somatic) cells are diploid, containing 2 sets of chromosomes (one from each parent)

  3. This process is required to produce egg and sperm cells for sexual reproduction

  
• Advantages of sexual reproduction

  • Diverse offspring: genetic variation among offspring (survival of species)
  • Half of the DNA comes from mom
  • Half of the DNA comes from dad
  • Genetic variation allows individuals within a population to have slight differences
  • Plants can resist diseases
  • Traits can develop to resist harsh environments that allows an organism survive
• Disadvantages of sexual reproduction

  • Time and Energy
  • Organisms have to grow and develop until they are old enough to produce sex cells
  • Search and find a mate
  • Searching can expose individuals to predators, diseases, or harsh environmental conditions
  • Fertilization cannot take place during pregnancy, which can last as long as 2 years for some mammals
• Asexual reproduction


  One parent: organism produces offspring without fertilization
• Uniform offspring


  Because offspring inherit all of their DNA from one parent, they are genetically identical to each other and to their parent
• Mitosis


  The nucleus of a cell divides to create 2 new nuclei, each containing an identical copy of DNA
• Cytokinesis


  The cell physically divides into 2 cells
• Modes of asexual reproduction

  • Fission
  • Budding
  • Regeneration
  • Vegetative Propagation
• Fission


  Cell division in prokaryotes that forms two genetically identical cells
• Fission


  1. DNA is copied

  2. The cell begins to grow longer, pulling the two copies apart

  3. The cell membrane pinches inward in the middle of the cell

  4. Cell splits to form two new uniform, identical offspring
• Fission


  • bacteria, E.coli, pond critters
• Budding


  • A new organism grows by mitosis and cell division on the body of its parent
  • The bud, or offspring is identical to the parent
  • The bud, when large enough, can break off of the parent and live on its own
  • Offspring may remain attached and form a colony
• Budding


  • Yeast, Hydra, cactus
• Regeneration


  Occurs when an offspring grows from a piece of its parent
• Regeneration


  • Sea Stars, sea urchins, sea cucumber, sponges, and planarians (producing new organisms)
  • Gecko, newts, tadpoles, crabs, hydra, and zebra fish (producing new body parts)
• Vegetative Propagation


  • Uniform offspring grow from a part of a parent plant
  • Parent plants sends out runners
  • Where the runner touches the ground, roots can grow
  • A new plant is produced even if the runner is broken apart
  • Each new plant is uniform and identical to the parent
• Vegetative Propagation


  • strawberries, potatoes, ivy, crabgrass
• Advantages of asexual reproduction

  • Enables organisms to reproduce without a mate
  • No wasted time and energy
  • Enables some organisms to rapidly reproduce a large number of uniform offspring
• Disadvantages of asexual reproduction

  • Because their offspring are identical, there is no genetic variation that can give an organism a better chance for survival
  • If a weed killer can kill the parent, it will also kill the offspring
  • A whole species can be wiped out from a disease
  • Dangerous mutations in DNA - if the parent has the mutation in their DNA, the offspring will have it too
• Conjugation


  • A form of sexual reproduction in bacteria where a bacterium transfers genetic material to another through direct contact
  • There is no male or female
• Conjugation


  • Bacteria, paramecia, spirogyra
• Zygospore


  The zygote in spirogyra develops a tough coat and is called a zygospore, which hatches when conditions are favourable
• Sexual reproduction in animals

  • Have males and females
  • Have sex organs (Gonads)
• Ovaries


  Produce ova or eggs (haploid)
• Testes


  Produce sperm (haploid)

  
• Hermaphrodites


  • Have ovaries and testes in the same animal
  • Occurs in slow or sessile organisms like worms, hydra, snails
  • Self-fertilization is rare
• Gametogenesis


  The production of sperm and eggs, including the process of haploid cells, and growth and maturation of these cells into oocytes and sperm

  
• Spermatogenesis


  The production of sperm

  
• Oogenesis


  The production of eggs

  
• Differences between sperm and egg

  • Sperm are small, many, and mobile (1-4 mm/min)
  • Eggs are larger, fewer, and non-mobile
  • Sperm have a complex shape
  • Eggs are round
  • Eggs may have yolk

  
• Fertilization


  1. Sperm swim to egg

  2. Sperm releases enzymes to make hole in egg

  3. Sperm injects nucleus into egg

  4. Fertilization membrane forms around egg

  5. No future fertilization

  6. Joining of sperm nucleus and egg nucleus to form diploid zygote

  
• Types of fertilization


  • External fertilization (outside female)
  • Internal fertilization (inside female)
• External fertilization


  • Female releases eggs in water, male releases sperm in water
  • Problems: sperm find eggs and many gametes made

  
• External fertilization


  • Spawning behaviour or Amplexus
• Seasonal spawning of salmon usually occurs from November to December, but may extend from October to late February in some areas, particularly larger rivers. About 90 to 95% of all Atlantic salmon die after spawning has taken place. Those that survive may spawn again. Female fish lay their eggs in gravel depressions known as 'redds'.
• Amplexus


  A type of mating behavior exhibited by some externally fertilizing species in which a male grasps a female with his front legs as part of the mating process, and at the same time or with some time delay, he fertilizes the eggs as they are released from the female's body
• Internal fertilization


  • Safer
  • Occurs in terrestrial animals and some aquatic organisms
  • Requires moist female reproductive tract
  • Fewer eggs needed
  • Gametes have short lifespan (24 hours)
  • Requires specialized organs
  • Timed release of gametes (hormonal)