GEN BIO FIRST LESSON (4TH QUARTER)

• Patterns of descent with modification

  From common ancestors to produce the organismal diversity observed today
• Fundamental concept of evolution

  • Populations and species of organisms evolve throughout time
• Charles Darwin


  British naturalist who authored "On the Origin of Species" in the 1850s, proposing that species evolve and all living organisms can trace their descent to a common ancestor
• Descent with modification


  Passing on of qualities from parents to offspring, known as heredity
• Gene


  Basic unit of heredity, a blueprint for producing an organism
• Darwin's sketch


  1. Shows how one species can branch into two over time, and how this process can repeat multiple times in the "family tree" of a group of related species

  2. Darwin referred to this process as "descent with modification", which we now call evolution
• Each species has a distinct set of heritable (genetic) differences from the common ancestor that have evolved gradually over very long time periods
• Repeated branching processes, in which new species split from a common ancestor, result in a multi-level "tree" that connects all living organisms
• The process of biological evolution is powerful and crucial, allowing organisms that are better adapted to their environment to continuously change life and making all living organisms in our world into what they are now
• Evolution is not a finished process in which humans are the end result, but a continuous process which has been modifying and shaping life on Earth for billions of years and will continue to do so for as long as organisms are born, die, and compete for what they require to survive and reproduce
• Reproductive isolation mechanisms


  A set of evolutionary mechanisms, behaviors, and physiological processes that are necessary for speciation and prevent members of different species from producing offspring or interbreeding, ensuring that any offspring are infertile
• Species


  Closely related organisms that are very similar and capable of producing fertile offspring
• Levels of reproductive isolation mechanisms

  • Prezygotic
  • Post-zygotic
• Prezygotic isolation


  Separation of distinct species in order to prevent gametes from forming a zygote and thereby producing offspring, occurring prior to zygote formation
• Pre-zygotic isolation mechanisms


  • Geographic or ecological or habitat isolation
  • Temporal or seasonal isolation
  • Behavioral isolation
  • Mechanical isolation
  • Gametic isolation
• Geographic, ecological, or habitat isolation


  Mating is prevented because species are separated due to differences in their habitat, even if their geographic ranges overlap
• Temporal or seasonal isolation


  Mating between two closely related species with overlapping ranges cannot occur due to a time difference in sexual maturity, such as one species breeding in winter and the other in fall, or one during daytime and the other at night
• Behavioral isolation


  Reproductive isolation based on species' behavior during mating rituals and signals, where differences in courtship practices prevent mating
• Mechanical isolation


  Differences in the reproductive organs of two species prohibit interbreeding and prevent the birth of a sterile hybrid
• Gametic isolation


  When a sperm cell from one species fails to penetrate the egg of another species due to chemical differences, preventing hybridization
• Gametic reproductive isolation is most common in organisms that reproduce externally, such as marine creatures and flowering plants, where sperm cells are transported in the water and may interact with eggs from different species
• Post-zygotic isolation mechanisms


  Factors that prevent the successful reproduction that occur after fertilization and the formation of a zygote, such as hybrid inviability, hybrid sterility, and hybrid breakdown
• Hybrid inviability


  A reproductive isolation that prevents the offspring of individuals from different species from being able to develop to reproductive maturity successfully, due to incompatible genetic material
• Hybrid sterility


  Individuals from distinct species are unable to produce functional gametes, creating inviable offspring while the other offspring are sterile, due to errors in the meiosis process and incompatibility between the chromosomes of the parent species
• Hybrid breakdown


  Mating of two different species produces hybrid offspring that are initially strong and fertile, but successive generations have lesser viability or are sterile, leading to reduced reproductive success and an established population