variation and evolution

• Definition of variation

  All the differences in the characteristics of individuals in a population
• Causes of variation

  1. Alleles inherited by individuals

  2. Environmental factors

  3. Combination of genes and the environment
• Environmental variation

  • Color of flowers depending on soil pH
  • Language variation in humans
• Combination of genetic and environmental variation

  • Height in humans
• In any population of a species, there is a massive amount of genetic variation due to mutations
• Mutations are random changes to DNA and most have no effect on the phenotype
• Some mutations can influence the phenotype, like alleles for tallness leading to tallness if the diet is suitable
• Some mutations can lead to a new phenotype, which can be beneficial if the environment changes
• In the 1950s, a virus hit the UK and killed 99% of wild rabbits


  A mutation occurred making surviving rabbits resistant to the virus, leading to a new phenotype
• Evolution


  Change in the inherited characteristics of a population over time through natural selection
• Life first developed on earth more than 3 billion years ago
• All species of living things have evolved from simple life forms
• Scientists believe that all species have evolved from simple life forms through evolution by natural selection
• Natural selection


  Process where individuals with advantageous traits are more likely to survive and reproduce, passing on those traits to offspring
• Genetic variation exists within a population of a species
• Alleles determine characteristics like fur thickness, eyesight, and hearing in rabbits
• Rabbits with alleles for thicker fur are more likely to survive in colder temperatures


  They are more likely to reproduce and pass on the alleles for thicker fur
• Rabbits with alleles for better eyesight or hearing have an advantage when a predator like a fox is present


  They are more likely to survive and reproduce, passing on the beneficial alleles
• Over many generations, advantageous alleles become more common in a population through natural selection
• Evolution is the change in inherited characteristics of a population over time through natural selection
• Two populations of one species can become so different in phenotype that they can no longer interbreed to produce fertile offspring


  These populations become two separate species
• Pygmy rabbits are so small that they cannot breed successfully with normal-sized rabbits, making them a different species
• Speciation occurs when two populations of one species become so different that they can no longer interbreed to produce fertile offspring
• Speciation will be covered in more detail in a later video for those studying biology
• Selective breeding

  1. Describing what's meant by selective breeding, also known as artificial selection

  2. Explaining the impact of selective breeding of food plants on domesticated animals

  3. Describing the disadvantages of selective breeding
• Examples of selective breeding

  • Domestic dogs have been selectively bred to have a gentle nature
  • Food crops such as wheat have been selectively bred to be resistant to disease
  • Animals such as cows have been selectively bred to produce more meat or milk
  • Certain plants have been selectively bred to produce large or unusual flowers
• Stages of selective breeding

  1. Select the largest male and female from a mixed population of cows

  2. Breed these together to produce offspring with variation

  3. Select the largest male and female offspring and breed them together

  4. Continue this process over many generations until all the offspring are large
• Inbreeding can cause some breeds to be prone to disease or inherited defects
• Problems caused by inbreeding

  • Dog breeds have been selectively bred for hundreds of generations and many develop inherited disorders such as joint problems, heart disease, or epilepsy
• Genetic engineering


  Genes from one organism are cut out and transferred to cells of a different organism to modify its genome
• Genetic engineering in medicine

  • Insulin production using genetically modified bacteria containing the human insulin gene
• Genetic engineering in agriculture

  • Production of genetically modified (GM) crops with greater yield, resistance to disease or insect attack, and other beneficial traits
• Some GM crops are resistant to herbicides, allowing farmers to kill weeds without harming the GM crop
• There are concerns about the safety of GM crops, including potential harm to insects, wildflowers, and the need for more research on the health effects of consuming GM crops
• Gene therapy


  Genetic modification as a way to treat inherited disorders in humans
• The long-term effects of gene therapy are not fully known, including potential effects on other genes
• Main steps in genetic engineering

  Identify the gene to transfer 2. Isolate the gene using enzymes 3. Transfer the gene into a plasmid or virus (vector) 4. Transfer the gene into the cells of the target organism at an early stage of development
• Transferring the gene at an early stage ensures that all cells receive the gene, leading to the development of desired characteristics
• Speaker: 'Music'
• Plants are cloned by cuttings or by tissue culture