Inheritance, Variation and Evolution

• 3 main causes of variation

  1. Alleles that individuals inherit - caused by genetic
  2. Environment e.g. language barriers
  3. Genes and Environment: e.g height - some have alleles which make them taller but diet must have calcium for strong bones
• What causes genetic variation?

  Mutation - random changes to DNA, takes place all the time, most don't affect phenotype but some can for e.g. alleles for tallness would happen if diet is good
• There can be beneficial phenotypes if environment changes and there's rapid changes to the species
• Life first developed on Earth more than 3 billion years ago - simple forms like single cells
• all species of living things have evolved from simple life forms - evolution by Natural Selection.
• Natural selection is the process through which populations of living organisms adapt and change to desired characteristics
• If a species with a specific characteristic survives an obstacle/difficulty, it will have a higher chance to reproduce more and alleles will be passed to the offspring
• Evolution

  the change in the inherited characteristics of a population overtime through natural selection
• Humans took wolves and by using selective breeding they produced dogs
• Four examples of selective breeding:

  Domestic dogs - bred to have a gentle nature

  Food crops - resistant to diseases

  Cows - more meat and milk

  Plants - large flowers
• How is selective breeding carried out? E.g cows for meat

  Take random population of cows, select the largest male and female

  Breed them together : produce large and small cows

  Select the largest male and female offspring and breed them together

  Continue until all offspring are large
• Problem with Selective Breeding

  If we breed together closely related animals or plants, we can get inbreeding which can cause some breeds to be prone to diseases or inherited defects
• Genes from one organism are cut out and transferred to cells of a different organism in genetic engineering
• Genetic engineering - can transfer genes to plants to get GM crops - produce greater yield than normal - resistant to diseases - produce bigger crops - can be resistant to herbicides so no crops damaged
• Steps in Genetic Engineering

  Find the gene we want to transfer

  Use enzymes to isolate the gene

  Transfer into plasmid - useful for transferring DNA from one organism to another

  The desired gene is transferred into cells of the target organism
• Always transfer the gene at an early stage in the development of an organism so then all cells in the organism can receive the gene and the organism is developed with desired characteristics
• Fossils

  Remains of organisms from millions of years ago found in rocks - provide evidence for evolution
• How fossils are formed?

  through the process of fossilisation, where the remains of plants or animals are gradually replaced by minerals in the ground over a long period of time.
• How are fossils formed? (2)

  When parts of organisms haven’t decayed - happens when conditions needed to decay cannot eg temperature is too cold, not enough O2 or H2O.
• How are fossils formed? (3)

  By preserved traces of organisms
• Problem with fossils

  Many of the earliest forms of life are soft-bodied organisms which rarely form fossils, many have been destroyed by changes to rock in the Crust - because of this scientists cannot predict how life began on Earth
• Species can be extinct:


  due to a catastrophic event

  environment changes

  new disease

  new predator - kills it - extinct

  if a new successful species evolves and competes with it eg for food
• A species is extinct when there are no remaning individuals of that species alive
• Bacteria evolves rapidly - reproduce every 30 minutes
• Many species died from diseases caused by bacteria - in 1940s doctors treated bacterial diseases by antibiotics like penicillin
• Antibiotics kill bacteria - is widely used in medicine and used in farming to prevent animals from getting bacterial diseases
• Few years ago, certain strains of bacteria are no longer killed by antibiotics - have evolved - antibiotic resistant
• How does antibiotic resistance happen?

  In a population of an organism, there will be genetic variation due to mutation and that makes a bacterium resistant to antibiotics

  If an antibiotic is taken - all bacteria's killed except bacteria that are resistant

  That bacteria survives and reproduces - the population rises and spreads
• To reduce Antibiotic-resistant development:

  Don't prescribe antibiotics inappropriately

  Must fully complete the course of antibiotics so all of it is killed - no mutation

  Restrict use of antibiotics in farming
• Scientists are trying to develop new antibiotics - time-consuming and expensive - due to increasing antibiotic resistant bacteria - hard to keep up
• 1700s- Carl Linnaeus classified species into different categories based on structure + characteristics - divided living organisms into 2 kingdoms (animal and plant) - then divided them into smaller categories
• Kingdom Phylum Class Order Family Genus Species - King Phillip came over for good soup
• Organisms named from their genus and species - called a binomial system
• Key fact: The classification system is based on characteristics
• We can use microscopes to look at internal structures - can also analyse organisms biochemistry for eg DNA and look for similarities with other species
• Carl Woese: Three domain system - compared the biochemistry of organisms to determine their evolutionary relationships
• Three domain system

  Archae: primitive bacteria found in extreme conditions

  True Bacteria: live in humans digestive system - truly good

  Eukaryota: animals, fungi
• Evolutionary Trees

  used to show how closely related organisms are - made by using the classification data on living organisms eg DNA

  Extinct organisms? Use fossils - but many fossil records aren't done
• Mitosis


  Cell division where one cell is copied into two identical cells
• Gametes


  Cells where the chromosomes are not paired, e.g. sperm and egg cells