Evolution

Evolution

1. Variation

   • Genetic variation
     • Characteristics determined by inherited genes
     • Combining of genes from two parents causes genetic variation
   • Environmental variation
     • Caused by the conditions something lives in
   • Genetic and environmental variation
     • E.g. some people are more likely to get certain diseases because of genes but lifestyle also affects risks
   • Mutations may also lead to changes in the characteristics that a protein codes for

2. Theory of evolution

   • All of today’s species have evolved from simple life forms that first started to develop over 3 billion years ago
   • Charles Darwin
     • All the individuals within a species show a wide range of variation for a particular characteristic
       • Some of these will be more suited to the environment than others
         • These will be more likely to survive and therefore more likely to breed successfully
           • The useful characteristic will be passed on to the offspring
   • New discoveries
     • Phenotype is controlled by genes
     • New genetic variants arise because of mutations
     • Beneficial genetic variants are passed on to future generations in the DNA that parents contribute to their offspring
     • Fossils of different ages show how organisms have changed over time
     • Evidence from bacteria evolving to become resistant to antibiotics
   • Natural selection (today’s theory)
     • Wide variation in characteristics due to the mix of genetic variants
       • Some genetic variants give rise to characteristics that’s are better suited to the environment- have a better chance of survival and are more likely to breed
         • Genetic variants responsible for useful characteristics passed on to next generation
   • Ideas about evolution
     • Controversy (Darwin)
       • Went against religious beliefs
       • He couldn’t explain why new characteristics appeared or how these where passed on
       • Not enough evidence
     • Lamarck
       • Thought that changes an organism acquires during its lifetime would be passed on to its offspring
         • Experiments didn’t support his hypothesis
           • Whereas the discovery of genetics supported Darwin’s idea

3. Speciation

   • Development of new species
     • Happens when populations of the same species become so different that they can no longer interbreed to produce fertile offspring
   • Species - group of similar organisms that can reproduce to give fertile offspring
   • When it occurs
     • Isolation
       • Populations of a species are separated due to a physical barrier e.g. floods and earthquakes
         • Can eventually lead to speciation
     • Natural selection
       • When 2 populations are isolated due to a physical barrier conditions on either side will be slightly different e.g. climate
         • Because the environment is different, different characteristics will become more common in each population
           • Each population shows genetic variation because they have a wide range of alleles
             • Individuals with characteristics that make them better adapted to their environment have a better chance of survival and are more likely to breed successfully
               • Alleles controlling the beneficial characteristics more likely to be passed ob
   • Alfred Russel Wallace
     • Came up with the idea of natural selection and published work on the subject with Darwin - this prompted him to publish ‘On the Origin of Species’
     • Evidence form travelling e.g. warning colours were a beneficial characteristic that had evolved by natural selection

4. Extinction

   • When no living individuals of a species remain
   • Causes:
     • The environment changes too quickly e.g. destruction of habitat
     • New predator kills them all
     • New disease kills them all
     • Can’t compete with another (new) species for food
     • Catastrophic event kills them all e.g. volcanic eruption

5. Selective breeding

   • When humans artificially select the plants or animals that are going to breed so the genes for particular characteristics remain in the population
     • To develop useful features e.g.
       • Animals that produce more meat of milk
       • Crops with disease resistance
       • Behaviour traits
   • Process
     • Select the ones with the desired characteristics
       • Breed them with each other
         • Select the best offspring and breed them together
           • Continue this process over several generations- desirable trait gets stronger and eventually all offspring will have the characteristic
   • Reducing the gene pool
     • Inbreeding - farmer breeds best animals or plants which are all closely related
       • More chance of inheriting harmful genetic defects
         • E.g. pugs often have breeding problems
     • Reduction in the number of different alleles
       • Less chance of any resistant alleles being present in the population

6. Genetic engineering

   • To transfer a gene responsible for a desirable characteristic from one organism’s genome into another organism so it has the desired characteristic
   • Useful gene isolated from one organism’s genome using enzymes and it is inserted into a vector
     • Vector - used to transfer DNA into a cell e.g. virus or bacterial plasmid
     • When the vector is introduced yo the target organism, the useful gene is inserted into its cell
   • Uses
     • Used to produce human insulin
       • Insulin gene cut out of human DNA using enzymes
         • Same enzymes cut the bacterial DNA and different enzymes are used to insert the human insulin gene
           • The bacteria are then allowed to multiply and the insulin produced while they grow is purified and used to treat people with diabetes
     • Genetically modified crops to improve quality of fruit or make them resistant to disease, insects and herbicides
     • Sheep have been genetically engineered to produce substances like drugs in their milk used to treat human disaeses
     • Scientists researching treatments for inherited disorders caused by faulty genes - gene therapy (insert working genes)

7. Cloning

   • Making a genetically identical copy of an organism
   • Plants
     • Tissue culture
       • A few cells are put in a growth medium with hormones and they grow into new plants - clones of the parent plant
       • Made quickly in little space and can be grown all year
         • Used by scientists to preserve rare plants that are hard to reproduce naturally
         • Used to produce lots of stock quickly
     • Cuttings
       • Plant cuttings taken from good parent plants to produce identical copies
       • Quite quick and cheap but only one produced per cutting
   • Animals
     • Embryo transplant
       • Embryo is created then split many times in the early stages to form clones - inserted into host mothers
       • Used by farmers to produce cloned offspring from the best bull and cow
         • Sperm cells taken from prize bull and egg cells from a prize cow - artificially fertilised
           • Embryo then split many times (before any cell becomes specialised)
             • Implanted into lots of other cows
     • Adult cell cloning
       • Nucleus removed from unfertilised egg and replaced with nucleus removed from adult body cell
         • Egg stimulated by electric shock causing it to divide like a normal embryo
           • Implanted into uterus when it is a ball of cells
   • Issues
     • Benefits
       • Creates lots of ideal offspring with known characteristics quickly
         • Ideal for farmers - can create animals with desired characteristics
       • Study of animal clones could lead to a greater understanding of the development of the embryo, ageing and age-related disorders
       • Could be used to preserve endangered species
     • Concerns
       • Reduced gene pool so fewer alleles in population
         • All closely related so could all be wiped out by a new disease if there is no resistant allele
       • Cloned animals may not be as healthy (Dolly the sheep had arthritis)
       • Worry that humans might be cloned in the future which could cause problems

8. Fossils

   • Remains of organisms from many years ago found in rocks
     • We can see how organisms have evolved
   • Formation
     • Gradual replacement from minerals
       • Parts such as bones don’t decay easily but are eventually replaced by minerals as they decay forming a rock-like substance in the shape of the original hard part
     • Casts and impressions
       • Formed when an organism is buried in a soft material such as clay which eventually hardens as it decays
     • Preservation in places where no decay happens
       • Microbes involved in decay need the right conditions in order to break down material: oxygen, moisture and right temperature and pH
         • If the conditions aren’t right decay won’t take place and the organism’s remains will be preserved e.g. in amber/ glaciers/ peat bogs
   • Origins of life on earth
     • Lack of evidence because:
       • Scientists believe many early organisms were soft-bodied - soft tissue decays away without forming fossils
       • Fossils may have been destroyed by geological activity

9. Antibiotic-resistant bacteria

   • Antibiotic resistance
     • Mutations can lead to changes in its characteristics e.g. being less affected by a particular antibiotic
       • Can lead to antibiotic-resistant strains forming as the gene for antibiotic resistance becomes more common in the population
         • Bacteria can evolve quite quickly as they reproduce rapidly
     • Resistant bacteria will live for longer and reproduce many more times
       • This increases the population size of the antibiotic-resistant strain
         • No effective treatment for these strains and so the infection easily soreads
           • Super bugs resistant to most known antibiotics are becoming more commonn
   • Spread of antibiotic resistance
     • Causes
       • Doctors prescribing antibiotics for non-serious conditions
       • Doctors prescribing antibiotics for viral infections
       • People not taking the full course of antibiotics
         • This ensures all the bacteria are destroyed so there are none left to mutate and become resistant
       • Antibiotic given to animals in farming to prevent illness and increase growth can lead to resistant bacteria which can spread to humans
     • Rate of development of new antibiotics is slow and costly