Variation and Selection

• Variation is the differences between individuals of the same species.
• Variation can be genetic and/or phenotypic.
• Genetic variation is the difference in genetics among individuals within the same species.
• Phenotypic variation is the variability of phenotypes within a population.
• Phenotypic variation can be caused in two main ways:

  • Genetic
  • Environmental
• Genetic variation in populations can be caused by verious factors:

  • Mutation
  • Meiosis
  • Random mating
  • Random fertilisation
• Continuous variation results in a range of phenotypes between two extremes.
• Continous variation is caused by both genes and the environment.
• Discontinuous variation results in a limited number of phenotypes with no intermediates.
• Discontinuous variation is usually caused by genes only.
• Continuous variation is when a trait can have many different values within a group of individuals.
• Discontinuous variation is when a trait can only have specific, distinct options without any in-between possibilities.
• Mutation is a genetic change.

  A gene mutation is a random change in the base sequence of DNA.
• The rate of genetic mutation can increase due to a variety of factors, including:

  • Ionizing radiation
  • Some chemicals
• Mutation is the way in which new alleles are formed.
• An adaptive feature is an inherited feature that helps an organism to survive and reproduce in it's environment.
• Hydrophytes are plants that are adapted to grow in or around water.
• Adaptive Features of Hydrophytes:

  • Wide, flat leaves to increase surface area to float near water surfaces and efficiently absorb more sunlight for photosynthesis.
  • Have small roots because they can absorb water directly through their leaves and stems.
  • Stomata mostly found on the upper side, allowing for efficient gas exchange.
• Xerophytes are plants that are adapted to survive in dry environments with limited water.

  These plants have adaptive features with allow it to maximize water uptake and minimize water loss.
• Adaptive features of Xerophytes:

  • Thick waxy cuticle to prevent water loss
  • Sunken stomata to reduce water loss
  • Thick stems or leaves that store water
  • Small leaves to reduce surface area for evaporation
  • Extensive roots to maximise water uptake.
• Natural Selection is the process by which the frequency of a particular allele in a population changes over time to help organisms survive and reproduce.
• Adaptation is the process, resulting from natural selection, by which populations become more suited to their environment over many generations.
• Antibiotic Resistance is the ability of bacteria to resist the effects of antibiotics due to mutation and reproduce rapidly.
• Selective breeding is a process where humans choose individuals with desdesirableirabel features with are then bred together to produce the next generation. Then, individuals displaying the desired features are further chosen from this new generation.
• Selective breeding, also known as artificial selection, is a method used ower multiple generations to enhance desirable traits in:

  • Crop plants
  • Domesticated animals
• Humans selectively breed plants to enhance various traits such as:

  • Disease resistance in food crops
  • Increased crop yield
  • Adaptation to challenging weather conditions
  • Improvement in taste and flavor of fruits
  • Cultivation of plants with large or unique flowers.
• Animals are selectively bred by humans to develop specific traits such as:

  • Livestock to have more milk or meat
  • Birds that lay large eggs
  • Domestic dogs with gentle nature
  • Sheep with good quality wool
  • Horses with fine features and great speed