6 - Variation and Evolution

• What is variation?


  - all the differences in the characteristics of individuals in a population
• What are the 3 main causes of variation in a population?

  - the alleles (genes) they have inherited (genetic causes)

  
  

  - the conditions in which they have developed (environmental causes)

  
  

  - a combination of genes and the environment.
• What is the variation like within a population of a species?

  
  

  What do all of these variants arise from?

  - usually, there is extensive, massive genetic varation within a population

  
  

  - all variants arise from mutations that most have no effect on the phenotype, some do influence phenotype, and very few determine a new phenotype
• Why might a mutation cause a new phenotype?

  - rarely, a mutation might give an individual a survival advantage (where the new phenotype is suited to an environmental change) which means they outsurvive others and go on to reproduce and therefore, pass this mutated, beneficial allele to their offspring
• What is evolution?

  - a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
• What does the theory of evolution by natural selection state?

  - that all species of living things have evolved from simple life forms which first developed over 3billion years ago

  - those best suited to an environmental change are more likely to survive and are more likely then, to reproduce and pass on their beneficial alleles to their offspring
• What happens when two populations of one species become too different?

  - if two populations of one species become so different in phenotype, they can NO LONGER INTERBREED TO PRODUCE FERTILE OFFSPRING

  - they have formed two new species
• What is selective breeding (aka artificial selection)?


  - selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics
• Why have domestic dogs been selectively bred?


  - to have a gentle nature
• Why have food crops been selectively bred?

  - disease resistance
• Why have animals such as cows been selectively bred?

  - to produce more meat or milk
• Why have certain plants been selectively bred?

  - to have large or unusual flowers
• What are the stages of selective breeding?

  1) From a mixed population, choose a male and a female with the desired characteristic.

  2) Breed this male and female together.

  3) From the offspring, breed together the male and female who show the desired characteristic the greatest.

  4) Continue this breeding over many generations UNTIL ALL THE OFFSPRING SHOW THE DESIRED CHARACTERISTIC.
• What is one problem of selective breeding?

  - if we breed together closely relatedanimals or plants, we can get 'inbreeding', which can cause somee breeds to be prone to disease or inherited defects
• What problems may an inbred dog have?

  - joint problems

  - heart disease

  - epilepsy
• What is genetic engineering?


  - process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
• Give an example of genetic engineering in plants.

  - plant crops have been genetically engineered to be resistant to diseases or to produce bigger, better fruits
• Give an example where genetic engineering has been used to treat a disease.

  - bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes
• What does genetic engineering in humans involve?

  - genes from the chromosomes of humans and other organisms can be cut out and removed, and then transferred to cells of other organisms
• What benefits do GM crops have?

  - genetically modified (GM) crop include ones that are resistant to insect attack or to herbicides

  - GM crops can also show increased yields
• Why may GM crops be unethical?

  - people have concerns about GM crops and their effect on populations of wild flowers and insects

  - some people feel the effects of eating GM crops on human health have not been fully explored
• How is genetic engineering being currently explored in medicine?


  - modern medical research is currently exploring the possibility of genetic modification to overcome some inherited disorders in humans (gene therapy)
• What are the main stages of genetic engineering?

  - enzymes are used to isolate the required gene

  - this gene is inserted intoa vector (usually a bacterial plasmid or a virus)

  - the vector is used to insert the gene into the required cells

  - genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they can develop with the desired characteristics
• Suggest why enzymes be used in genetic engineering to isolate the required gene?

  - the active site on enzymes can be modified to fit onto specific substrates
• Suggest why the genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development?

  - these cells have not differentiated yet

  - this means that all of the cells receive the transferred gene

  => organism develops with the desired characteristic
• What are clones?

  - organisms that are genetically identical to the parent
• What key advantage does cloning plants have?

  - we know that the clone will be genetically identical to the orginal plant => we know exactly what the clone's characteristics will be
• How can we clone a plant by taking cuttings?

  - an older, but simple, method used by gardeners to produce many identical new plants from a parent plant

  
  

  1) Remove a small piece of the plant.

  2) Dip the end into rooting powder (which contains plant hormones, this encourages the plant to develop roots).
• How can we clone a plant to produce hundreds of clones?


  - use tissue culture

  
  

  1) Take a plant that we want to clone and we divide the plant into hundreds of tiny pieces (each has a small number of cells).

  2) Incubate these small groups of cells with plant hormones (which stimulate the plant to grow and develop into fully-grown plants).
• Why must the conditions used for tissue culture be sterile?

  - we do not want to introduce any microorganisms such as bacteria or fungi
• What can tissue culture be used for?

  - commercially in plant nurseries to produce thousands of genetically identical plants quickly and cheaply

  - to preserve rare plant species (no extinction)
• What are the stages of an embryo transplant?

  - start with a sperm and an egg cell from the animal with the desired characteristics

  - fertilisation produces a fertilised egg cell

  - allow the fertilised egg to develop into early stage embryo (none of these cells have started to differentiate)

  
  

  - use a glass rod to split this embryo into two

  
  

  - transplant the two embryos into host mothers => embryos will grow and develop into two identical offspring (clones)
• What is one key disadvantage to animal cloning via embryo transplants?

  
  

  Why does adult cell cloning overcome this disadvantage?

  - we start with a sperm cell and an egg cell so we cannot be certain that the offpring will have the characteristics that we want

  
  

  - adult cell cloning uses an adult so we know the characteristics that the clone will have
• What are the stages of adult cell cloning?

  - nucleus is removed from an unfertilised egg cell of a species of animal

  
  

  - nucleus from an adult body cell, e.g. a skin cell, of the same species of animal, is removed and inserted into the initial egg cell

  
  

  - an electric shock stimulates the egg cell to divide to form an embryo

  - these embryo cells contain the same genetic information as the adult skin cell

  
  

  - when the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development => genetically identical clone to original mother, not host mother
• What did Charles Darwin do?


  - as a result of observations on a round the world expedition, backed by years of experimentation and discussion and links to developing knowledge of geology and fossils, proposed the 'theory of evolution by natural selection
• What 3 things did Darwin's theory suggest?


  - individual organisms within a particular species show a wide range of variation for any characteristic

  - individuals with characteristics most suited to the environment are

  more likely to survive to breed successfully

  - the beneficial characteristics that have enabled these individuals to survive are then passed on to the next generation
• What year did Darwin publish 'On the Origin of Species'?


  1859
• What are 3 reasons to why Darwin's theory of evolution by natural selection was controversial, and only gradually accepted?

  - the theory challenged the idea that God made all the animals and

  plants that live on Earth

  - there was insufficient evidence at the time when the theory was published to convince many scientists

  - the mechanism of inheritance and variation was not known until

  50 years after the theory was published
• What incorrect conclusion did Jean-Baptiste Lamarck suggest?

  - idea that changes that occur in an organism durings its lifetime can be inherited

  
  

  - e.g. everytime a giraffe used its neck, it would stretch and get longer, and the offspring would inherit this longer neck
• What did Wallace do?


  - Alfred Russel Wallace independently proposed the theory of evolution by natural selection

  - he published joint writings with Darwin in 1858 which prompted Darwin to publish 'On the Origin of Species' (1859) the following year