variation and evolution

• interaction with our environment can change our phenotype; smoking, sleep, sun exposure
• mutations may cause the coded protein to be different so changes the phenotype; this may be beneficial, making them more likely to survive and therefore reproduce to pass their genes onto the next generation - survival of the fittest by Charles Darwin
• natural selection is the process by which individuals with traits that are better suited to their environment survive and reproduce
• evolution: inheritance of a certain characteristic in a population, over multiple generations could lead to a change in the whole species
• Lamarck's early theory of evolution suggested that organisms could acquire new traits during their lifetime, and that these traits could be passed to their offspring
• Charles Darwin and Russel Wallace

  Charles Darwin made a number of important observations:

  1. Individual organisms within a species show a wide range of variation for a specific trait.
  2. Darwin observed variations between species adapted to different environments.
  3. Older layers of rock contained fossils of less complex organisms, while more recent layers showed more complex organisms.
• Many people didn't accept Darwin and Wallace's theory, for several reasons:

  • Religious reasons - Darwin's theory challenged the religious belief that God created all life forms.
  • Lack of evidence - a lack of hard evidence made many scientists hesitant to accept Darwin & Wallace's theory.
  • DNA hadn't been discovered yet the mechanism for inheritance and variation, now understood through genetics, was unknown during Darwin's time.
• Widespread genetic screening also has some potential drawbacks:

  1. Learning about their genetic risks can cause stress and mental health issues for some people.
  2. Genetic discrimination may lead to unfair treatment in jobs and insurance for those with certain gene variants. Strict regulations are needed to prevent gene-based bias.
  3. There are concerns about the misuse of genetic data by employers and insurers, emphasising the need for privacy protections.
• Why is the human genome important?

  1. It helps us understand how genetic diseases work so prevention steps can be taken. People can get screened to detect health risks early and start treatment sooner.
  2. It aids the diagnosis and treatment of inherited disorders by letting us quickly identify faulty genes. New personalised drugs and therapies can be tailored to a patient's specific genetic makeup (this is sometimes called personalised medicine).
• transgenic organism

  An organism with DNA from another species
• cloning vs selective breeding

  All offspring are identical / no variation

  It is faster

  More offspring are produced 

  There is no need for natural mating / no need to keep two parents
• 1. Find a plant with desirable characteristics that you want to clone.
  2. Take very small pieces of plant tissue (called explants) from the tips of stems.
  3. Sterilise the explants to remove any microorganisms.
  4. Place the explants in a agar plate and let them grow into small masses of cells called calluses. The nutrient medium should also contain growth hormones. 
  5. Transfer the calluses to soil where they can grow into plantlets (basically baby plants).
  6. The plantlets can then be transferred to their own pots to develop into genetically identical adult plants.
• cuttings vs micropropagation

  Cuttings is quicker

  Cuttings is cheaper

  Cuttings requires less technical expertise/equipment

  Don't have to worry about sterilisation so much for cuttings 
• nitrates needed for amino acids, proteins, DNA, genetic material

  phosphates for DNA, genetic material, cell membranes etc

  glucose/ sucrose for energy, respiration

  magnesium for chlorophyll, chloroplasts
• micropropagation to clone plants

  1. Cut a small piece of plant tissue, an explant, from the tips of stems, and sterilise them to remove microorganisms.
  2. Place the explants in a petri dish that contains agar jelly with growth hormones and nutrients like glucose and mineral ions.
  3. Once they grow a bit into calluses, transfer them to soil so they can grow into plantlets.
  4. Finally transfer them to their own pot. Ensure that the whole process is done at a reasonable temperature and that the plants get enough light and water.
• Fossils are the remains of organisms from millions of years ago, which are found in rocks.
• how do fossils form

  1. Hard body parts, such as bones and shells, which decay very slowly, are gradually replaced by minerals, forming rock-like substances.
  2. Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock.
  3. Some parts of organisms may not decay at all. For example, dead animals and plants can be preserved in amber, peat bogs, tar pits, or in ice.
• The lack of oxygen means that microorganisms can't respire aerobically and so can't carry out the decay process.

  therefore are preserved in a tar pit
• extinction

  Rapid environment change such as an increase in temperature

  Reduction in habitat as it could reduce food and living space

  Increase hunting as individuals are directly killed 

  The spread of a new disease 

  Introduction of a new competitor or predator 

  A catastrophic event, such as an asteroid strike 
• Wallace is best known for two things:

  1 Studying warning colouration in animals, for example in the Golden Birdwing Butterfly.

  2 His theory of speciation.
• A species is defined as a group of genetically similar organisms that are able to interbreed and produce fertile offspring.

  2Speciation means the formation of a new species.

  This can happen when different populations of the same species become so different that they are unable to interbreed and produce fertile offspring anymore, at which point they are considered different species and we say speciation has occurred.
• Speciation may occur due to a combination of both isolation, and natural selection. Isolation happens when a physical barrier (such a new river or mountain range) separates two different populations of a given species.

  The environment may be different on either side of the barrier. For example the climate or food sources on either side of a mountain range may be different.
• A species is a group of organisms that are able to interbreed and produce fertile offspring.
• antibiotic resistance is become more common

  Doctors often prescribe antibiotics in cases where they aren't necessary. For example, mild or viral infections

  Many people don't take the full course of antibiotics, so not all the bacteria are killed

  Huge amounts of antibiotics are given to farm animals in order to make them grow faster
• antibiotic resistance

  A population of a bacteria infect somebody antibiotics taken to kill the bacteria

  random mutation makes bacteria less effective to the antibiotic than others

  The antibiotics kill all the bacteria except those that are resistant

  The resistance strains of bacteria now have more resources to grow and multiply 

  More mutations may arise, leading to greater resistance

  There is now a strain of bacteria that can't be killed by antibiotics

  more bacteria resistant to antibiotics = cant treat infections; more people will die of bacterial infections 
• the Linnaean system was developed by Carl Linnaeus, an international system to classify living organisms
• Kingdom

  phylum

  class

  order

  family

  genus

  species
• 1. Genes from chromosomes are ‘cut out’ using restriction enzymes leaving ‘sticky ends’ - short sections of exposed, unpaired bases
  2. A virus or bacterial plasmid is cut using same restriction enzyme to also create sticky ends containing antibiotic marker gene.
  3. loop and gene sticky ends join together by DNA ligase enzymes
  4. combined loop is placed in a vector (bacterial cell), multiplies containing modified gene. observe ones resistant to antibiotics.
  5. colonies produce modified gene too - inserted together. In plants vector is put into meristems to produce identical copies of modified plant.
• Genetically modified crops:

  • They are engineered to be resistant to insects and to herbicides.
  • This will result in increased yields as less crops will die.