Inheritance, variation and evoloution 

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  • Inheritance, variation and evoloution
    • Sexual and asexual reproduction
      • Asexual
        • One parent
        • No fusion of gametes
        • Produce genetically identical offspring by mitosis
        • Advantages
          • Faster
          • More time and energy efficient
          • Only one parent needed
        • Reproduce in different ways
          • Strawberry plants send out runners to touch ground and grow new plant
      • Sexual
        • Fusion of male and female gametes
        • Mix of genetic information-variation
        • Formation of gametes involves meosis
          • Copies of genetic information are made
            • Cell divides twice to form four gametes, each with a single set of chromosomes
              • All gametes genetically different from each other
          • Important because each gamete has half amount of chromosomes meaning that in fertilisation, the full genetic material is restored
        • Advantages
          • if enviroment changes, some offspring will be suited and survive
          • Allows humans to selectively breed for food production
      • Some organisms can produce both ways
        • Fungi make spores using both
        • Malaria parasites produce sexually in mosquito and asexually in humans
        • Given the choice, organisms prefer to produce asexually
    • DNA and protein synthesis
      • The Genome
        • Genetic material in nucleus is made of chemical called DNA
          • Contained in chromosomes
        • A gene is a small section of DNA
          • Each gene codes for a particular sequence of amino acids to make a specific protein
        • The whole genetic makeup of a organism is the genome
          • Because the human genome has been studied it may be important in the future
            • search for genes linked to disorders
            • understand inherited disorders and how to treat them
            • investigate how humans have changed over time
      • Structure of DNA
        • DNA is a polymer made from repeating units called nucleotides
          • Each nucleotide consists of:
            • A sugar
            • A phosphate
            • One of four bases: A,C,G or T
          • Each molecule has 2 alternating sugar and phosphate strands
            • Twisted to form a double helix
            • Attached to each sugar is a base
              • The attraction between certain bases holds the strands together
                • C links with G and T links with A
      • Making protiens
        • The order of bases controls the order of amino acids
        • A sequence of three bases is the code for one amino acid
        • Proteins synthesised in ribosomes
          • Carrier molecules bring amino acids to add to protein chain in right order
            • Protein chain folds into unique shape once complete
              • Shape allows proteins to function as enzymes, proteins or hormones
      • Mutations
        • A change in DNA structure
        • Changing bases of DNA can change order of amino acids
        • Mutations can cause the protein to change shape
          • If it's enzyme, the substrate may not fit into active site
          • Structural proteins may loose strength
        • Mutations can be useful
          • Without mutations variation and evolution through natural selection wouldn't occur
        • Certain chemicals and high level radiation can increase rate of mutations
    • Patterns of inheritance
      • Gregor Mendel
        • Investigated whether sexual reproduction produced a blend of characteristics on pea plants
        • Found characteristics were formed by units that were inherited
        • Scientists realised that chromosomes and the way Mendel's units worked were very similar
        • Units are now known as genes and are located on chromosomes
        • The importance of Mendel's discovery was not recognised
          • He was a monk not a scientist at university
          • Didn't publish work in well known book/journal
      • Modern ideas about genetics
        • Some characyeristics are controlled by a single gene
        • Sometimes there are two forms of a gene called alleles
          • One from mother
            • The combination of genes is called a genotype
              • One from father
              • What we see is called the phenotype e.g blue eyes
          • One from father
          • Homozygous- two alleles are the same
          • Hetrozygous is when two alleles are different
          • Alleles can be dominant or recessive
            • Dominant alleles are expressed even if there is only one copy
            • Recessive alleles are only expressed if there is two
      • genetic crosses
        • Punnet squares can predict the likelyhood that offspring will inherit characteristics
          • Capital letter s are used for dominant genes
            • Small letters are used for recessive genes
          • To work out the chances see how many capitals there are and put that number over 4
      • Sex determination
        • only one out of 23 pairs of chromosomes determine sex
        • Males have XY
          • Females have **
        • You inherit one from each parent, X from mum and X or Y from dad
    • variation and Evolution
      • Variation
        • Differences of characteristics in an individual
          • may be due to:
            • Genetics
            • Enviroment
            • Combination of genetic and enviroment
      • Natural selection
        • Evolution is the gradual change of characteristics of a population inherited over time
          • This can lead to the formation of new species
        • Most scientists support darwins 'natural selection theory'
          • On an around the world trip he made 4 observations
            • Organisms produce large numbers of offspring
            • Populations usually stay about the same size
            • Organisms show variation
            • Characteristics can be inherrited
        • Lots of people didn't believe Darwin's theory
          • Challenged the idea that god made the organisms on earth
          • Not enough evidence
          • Mechanism of inheritance and variation wasn't known until 50 years later
      • Evidence for evolution
        • Fossils are the remains of organisms found in rocks
          • Can be formed from:
            • Hard parts of animals that don't decay easily
            • Parts of organisms that haven't decayed because conditions were absent
            • As preserved traces of organisms e.g. fottprints
        • There are gaps in the fossil record because
          • Early forms of life were soft bodied meaning they left little trace
          • Traces may have been destroyed by geological activity
        • Development of antibiotic resistant strains
          • Bacteria reproduce at a fast rate
            • When they reproduce, mutations occur
              • Some mutated bacteria may be resistant to bacteria
                • These survive and reproduce so a resistant strain develops
    • Manipulating genes
      • Selective breeding
        • Can be used to
          • Make food crops from wildplants
          • Make domestic animals from wild ones
        • Humans breed organisms with particular, desirable genetics
          • Disease resistance in food crops
          • Animals that produce more meat or milk
          • Domestic dogs with a gentle nature
          • Large or unusual flowers
        • Choose parents that show desired characteristsic
          • Breed them together
            • From offspring choose those with desired characteristsics
              • Continue over generations
      • Genetic engineering
        • More recent way of changing organims
        • Enzymes are used to isolate required gene
          • Inserted into vector- bacterial plasma or virus
            • Vector is used to insert the gene into required cells
        • Plant crops have been genetically engineered to:
          • Be resistant to diseases
          • Produce bigger or better fruits
        • Fungi and bacterial diseases have been genetically engineered to produce useful subastances
          • Human insulin to treat type 1 diabetes
          • In the future, genetic engineering may be used to treat inherited diseases
      • Cloning
        • Clones are genetically identical individuals
        • In plants, Identical plants can be produced from
          • cuttings-used by gardeners
          • tissue culture- small groups of cells used to grow new plants
        • Cloning in animals
          • Remove nucleus from unfertilized egg cell
            • Insert nucleus
              • Stimulate egg cell to divide using electric shock
                • Allow resulting embryo to develop into a ball of cells
                  • Insert embryo into a surrogate womb of a female so it can continue to develop
    • Classification
      • Principles of classification
        • Linnaeus classified things into:
          • Kingdom - Phylum - Class - Order - Family - genus - species
        • Organisms are named by their binomial system
          • First part is their genus
          • Second part is their species
        • New models of classification  were proposed because:
          • Microscopes improved- scientists learnt more about cells
          • Biochemical processes became better understood
        • Due to genetic evidence, there is now a three domain system:
          • Archaea (Primitive bacteria)
          • Bacteria (true bacteria)
          • Eukaryota (Protists, fungi, plants and animals)
      • Extintion
        • Can be caused by:
          • Changes to enviroment
          • New predators
          • New diseases
          • New, more successful competators
          • Single catastrophic event
      • Evolutionary trees
        • A method used by scientists to show how they think organisms are related
        • Use current classification data for living organisms and fossil data for extinct organisms
      • Speciation
        • How new species develop:
          • Populations become physically isolated from eachother
            • Genetic variation is present between two populations
              • Natural selection operates differently in the two populations
                • Populations become so different that successful interbreeding is not longer possible

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