Inheritance and Variation

Cards (34)

  • Sexual reproduction involves the fusion of male and female gametes
    o in animals: sperm and egg cells
    o in flowering plants: pollen and egg cells
  • Asexual reproduction involves only 1 parent and no fusion of gametes
    o there is no mixing of genetic information
    o genetically identical offspring produced (clones) – identical to the parent and other offspring
    o only mitosis involved (no meiosis) – parent cell divides by mitosis producing 2 daughter cells
    o occurs in bacteria, some plants and some animals
  • Meiosis Process (involves 2 cell divisions)
    o chromosomes are duplicated (has double the amount of genetic
    information) – 92 chromosomes overall
    o cell divides in 2, each with half the number of chromosomes – 46
    chromosomes in each cell
    ▪ the chromosome pairs line up in the middle of the cell
    ▪ the pairs are pulled apart, each cell only has one copy of each
    o cells divide again producing 4 daughter cells23 chromosomes in each cell
    • The gametes produced are all genetically different due to the chromosomes being
    “shuffled” during meiosis
  • The genetic material in the nucleus of a cell is composed of DNA
    o DNA is a polymer made up of 2 strands forming a double helix
    o DNA is contained in structures called chromosomes
    o a gene is a small section of DNA on a chromosome
    o each gene codes for a sequence of amino acids to make a specific protein
  • DNA is a polymer made up of 4 nucleotides
    o each nucleotide is made of a sugar molecule (deoxyribose), a
    phosphate molecule and one base
    o the 4 bases are Guanine, Cytosine, Adenine and Thymine
    o G-C and A-T always link (complementary strands)
  • A sequence of 3 bases (a codon) is the code for a particular amino acid
    o the order of the bases control which amino acids are assembled
    to produce a protein
    o there are 20 amino acids
    • there are parts of DNA that don’t code for proteins, they instead control whether a gene is expressed or not
  • Protein synthesis
    • the process of producing a protein from the DNA
    o DNA is too large to move out of the nucleus
    o the 2 strands pulled apart and mRNA (messenger) matches the complementary base on the strand
    o the template of the DNA (mRNA) moves out of the nucleus and into the cytoplasm
    o tRNA (transfer) pulls the mRNA to the ribosomes where the codons on the mRNA are read and the
    corresponding amino acids are brought to the ribosome by carrier molecules
    o the amino acids connect together to form a protein, once the chain is complete the protein folds forming
    a unique 3D structure
  • There is 3 ways the sequence of DNA can mutate
    o Insertion
    ▪ a new base is inserted into the DNA base sequence
    ▪ as they are read in 3s this changes the way it is read and the amino acids coded for after the
    insertion
    o Deletion
    ▪ similar effect to insertion, just a base is removed from the sequence
    o Substitutions
    ▪ a base is changed, this may change which amino acid is coded for
    ▪ this doesn’t affect the amino acids coded for before or after the affected base
  • Homozygous – when both inherited alleles are the same e.g. both dominant or both recessive
    • Heterozygous – when one of the inherited alleles is dominant and the other is recessive
    • Genotype – the combination of alleles an individual has e.g. Bb
    • Phenotype – the physical characteristics that are observed e.g. eye colour
  • o Polydactyly (having extra digits – fingers or toes)
    ▪ caused by a dominant allele
    o Cystic Fibrosis (disorder of cell membranes causing increased production of mucus)
    ▪ caused by a recessive allele
    ▪ means that both parents either need to be carriers (have 1 of the recessive alleles so don’t
    express it) OR one parent have CF and the other be a carrier
    o Huntington’s Chorea (affects nervous systems causing involuntary muscular movement)
    ▪ caused by a dominant allele
    ▪ age of onset is about 35-40 years old (so may already have children passing on the alleles)
  • Embryonic screening allows scientists to observe whether the child will have a genetic condition or not – there
    are 2 methods:
    o amniocentesis – at 15 weeks the fluid from the sack around the foetus or foetal cells are sampled
    o chorionic villus sampling – at 10-12 weeks a small sample of tissue from the placenta is screened
  • Variaition - Differences in the characteristics (phenotype) of individuals in a population
  • Variation is caused by
    o inherited genes (genotype)
    genes are passed on from the parents
    ▪ the combining of genes from the mother and father creates genetic variation
    ▪ only identical twins have the same genotype
    ▪ e.g. eye colour, blood group, inherited disorders
    o conditions in which they have developed (environmental causes)
    ▪ the conditions the organism grows and developed in also affects its appearance
    ▪ e.g. scars in animals, smaller/yellow leaves in plants
  • Evolution: change in the inherited characteristics of a population over time through natural selection (which may
    result in the formation of a new species)
  • Theory of evolution: all species of living things today have evolved from life forms that first developed over 3 billion years ago
  • speciation
    o where 2 populations of a species becoming so different in phenotype that they can no longer successfully interbreed to produce fertile offspring (reproductively isolated) they have formed 2 new species
  • Selective Breeding Process
    • choosing parents with the desired characteristics from a mixed population
    • breading the chosen parents
    • from the offspring those with the desired characteristics are bred together
    • this is repeated over many generations until all the offspring show the
    desired characteristic
  • Genetic Engineering Process ( bacterial cell example)
    insulin producing gene from a chromosome isolated using a restriction enzyme
    • a plasmid is removed from a bacterial cell using lysozyme enzyme (this will be the vector to carry the gene)
    • a restriction enzyme is used to remove gene from the plasmid which is replaced with the insulin-producing gene
    from the human – the plasmid is now a recombinant plasmid
    DNA ligase enzymes are used to join the ends of the DNA
    • as the transgenic bacterium divide the offspring will carry the same gene meaning they can all produce insulin
  • Methods of plant cloning
    Tissue culture – important to preserve rate plate species or commercial growth in plant nurseries
    o a small group of cells are put in a growth medium with nutrients and growth hormones
    o they grow into new plants (clones of the parent plant)
    Cuttings – older, simpler method used by gardeners/horticulturists (cheaper)
    o a section of the stem (a cutting) is taken from a plant with a desirable trait
    o the cutting is planted, and the plants produced are clones of the original
  • Embryo transplants
    o sperm and egg cells from parents with desirable features are obtained (female sometimes given
    hormones to promote release of multiple eggs)
    o the egg cell is artificially fertilised in a lab to gorm an embryo
    o the embryo(es) is inserted into host mother(s), the offspring produced are all genetically identical with
    the desirable features – huge increase in the number of offspring an animal can produce
  • • Adult cell cloning
    o the nucleus is removed from an unfertilised egg cell
    o the nucleus from an adult body cell e.g. a skin cell is inserted into the egg cell
    o an electric shock stimulates the egg cell to divide forming an embryo
    o the embryo cells contain the same genetic information as the adult skin cell
    o the embryo can be inserted into the womb of an adult female to continue its development
  • Theory of Evolution:
    Individual organisms within a particular species show a wide range of variation for a
    characteristic due to mutations in DNA
    ▪ Individuals with characteristics most suited to the environment are more likely to survive to
    breed successfully (survival of the fittest)
    ▪ the advantageous characteristics are then passed onto future generations, over many
    generations the frequency of the advantageous characteristics increases with the population
  • Speciation: process of a new species developing through genetic variation causing 2 populations to no longer
    being able to successfully interbreed to produce fertile offspring
    Species: group of similar organisms that can reproduce to give fertile offspring
  • theory of speciation
    o variation exists within a population due to genetic mutations
    o alleles which provide a survival advantage become more abundant due to natural selection
    o populations of a species can become isolated e.g. due to a physical barrier
    o different alleles are advantageous in the new environment leading to more natural selection
    o overtime, the selection of different alleles increases the genetic variation between the 2 populations
    o when the 2 populations can no longer breed together to produce fertile offspring, a new species has formed
  • Formation of fossils
    mineralisation (gradual replacement by minerals)
    o teeth, shells and bones don’t easily decay so remain intact a long time after being buried
    o they are eventually replaced by minerals as they decay
    o this forms a rock-like substance which remains distinct from the remaining sedimentary rock
    casts
    o when an organism is buried in soft material e.g. clay, the clay hardens around it
    o when the organism decays there is a cast of the organism (often plant roots or an animal’s burrow)
  • More formation of fossils
    impressions
    o footprints can be pressed into materials when they are soft, so they leave an impression when the rock hardens
    • preservation (decay of an organism may not occur due to one or more of the conditions for decay are absent)
    o in glaciers it is too cold for decay microorganism to work
    o in peat bogs it is too acidic for decay microorganisms to work
    o in amber (yellow “stone” made from fossilised resin) and tar pits there is no oxygen or moisture, so decay microorganisms die
  • fossils can’t be used to tell us how live started on Earth because
    o most early life forms were soft-bodied, so they decayed completely
    o any traces left have been destroyed by geological activity e.g. crushed due to movement of tectonic plates
  • Extinction - when there are no remaining individuals of a species still alive
    Causes:
    environment changes too quickly so the species is unable to adapt fast enough
    new predators migrate to the area (often humans)
    new disease arises which they have no resistance too
    competition with another species for food which had advantageous mutations for the same food source
    • a catastrophic event e.g. a volcanic eruption or collision with an asteroid
    • destruction of habitat (often deforestation)
  • Process of Resistant Bacteria
    • bacteria can evolve rapidly due their rapid reproduction rate (every 20 minutes in the optimum conditions)
    mutations of bacterial pathogens produce new strains
    • some strains may be resistant to antibiotics, so are not killed (an advantageous characteristic)
    • they survive and reproduce, so the population or resistant bacteria increases rapidly (natural selection)
    • the strain then spreads rapidly as people aren’t immune to it and there is not effective treatment
  • Reducing the rate of development of antibiotic resistant strains of bacteria
    • antibiotics should not be given for viral or non-serious infections
    specific antibiotics should be given for specific bacteria
    • patients should complete their course of antibiotics – if they don’t some bacteria may survive and mutate to
    become antibiotic resistant
    reduced use of antibiotics in agriculture (used to prevent livestock dying of disease) – its overuse leads to
    antibiotic resistant bacteria are then transferred to humans when they consume the animals
  • Carl Linnaeus in the 1700s classified living organisms into:
    Kingdom
    Phylum
    Class
    Order
    Family
    Genus
    Species
  • Carol Woese developed the ‘3-domain system’, an addition to the Linnaean system
    archaea (primitive bacteria e.g. extremophiles in extreme pressure or temperature)
    bacteria (true bacteria e.g. E. coli – has different biochemical processes than archaea)
    eukaryota (broad range including animals, plants, protists and fungi – have nucleus
    enclosed in membranes)
  • Gamete – an organism’s reproductive cell which has half the number of chromosomes
    • Chromosome – a structure in the nucleus made up of a long strand of DNA
    • Gene – short section of DNA that codes for a protein
    • Allele – the different forms of the gene
    o Dominant – allele is always expressed
    o Recessive – allele is only expressed if the dominant allele isn’t present
  • In meiosis why are the gametes produced all genetically different?
    Chromosomes shuffled during meiosis