variation and evolution

• variation is all the differences in characteristics of individuals in a population; there are 3 main causes of variation.
• the three main causes include the alleles that individuals have inherited, this is a genetic cause. variation is also caused by the environment e.g. some flowers colours depend on the pH of the soil or in humans, languages are caused by the environment. some variation is a combination of genes and the environment e.g. height, some people may have alleles causing them to grow taller, but they must also have enough calcium for their bones to develop.
• genetic variations happen because of mutations. mutations are random changes to DNA. they happen all the time and most have no effect on the phenotype, some can influence the phenotype.
• very rarely, a mutation can lead to a completely new phenotype, sometimes this can be beneficial if the environment changes.
• genetic variation is about the alleles, this is called your nature. environmental variation are due to the environment you live in, this is called nurture.
• the are millions of species on earth currently, not including the millions of bacteria.
• scientists believed that life formed on earth more than 3 billion years ago, these first life forms were very simple e.g. single celled. all species of living things have evolved from these simple life forms. this process is called evolution by natural selection.
• e.g. every rabbit will have a slightly different combination of alleles that it has inherited from its parents, this could be thick fur, better eyesight etc. now if the environment gets colder, rabbits that have inherited alleles for thick fur are more likely to survive than the animals with alleles for thin fur. then, because these rabbits with thicker fur will survive, they are more likely to go and reproduce, their offspring are more likely to inherit thicker fur and the process continues. this is natural selection. over generations, the alleles for thicker fur will become more common.
• evolution is the change in the inherited characteristics of a population over time through a process of natural selection
• sometimes 2 populations of 1 species can become so different in phenotype, that they can no longer interbreed to produce fertile offspring. these 2 populations have become 2 separate species. e.g. normal rabbits and pygmy rabbits
• there are 4 types of selective breeding; selective breeding for a gentle nature e.g. dogs, to be disease resistant e.g. food crops, to produce more products e.g. cows and to have large or unusual flowers e.g. plants
• e.g. if we wanted to breed large cows for lots of meat we would

  1. take a mixed population of cows and select the largest male and female
  2. we would then breed these together, as we know sexual reproduction produces variation in offspring
  3. offspring will be a mixture of larger and smaller animals
  4. then select largest male and female offspring and breed these together
  5. we repeat this over many generations until all the offspring are large
• if we breed together closely related animals or plants, then we can get inbreeding. inbreeding can cause some breeds to be prone to disease or inherited defects.
• dog breeds have been selectively bred for many generations, lots of dogs develop inherited disorders like joint problems, heart disease and epilepsy.
• in genetic engineering, genes from one organism e.g. humans, are cut out and transferred to cells of a different organism e.g. bacteria. the genome of the bacteria is modified and now includes a human gene.
• insulin is a hormone involved in blood glucose regulation in humans. people with type 1 diabetes cannot make their own insulin so need to inject themselves with it regularly. bacteria have been genetically modified to contain the human insulin gene. these bacteria now produce human insulin, this insulin can be purified and used for type 1 diabetes.
• we can also transfer genes into plants to produce genetically modified (GM) crops. generally, GM crops produce a greater yield than normal crops. we can make GM crops resistant to disease or insect attack, or to produce bigger and better fruits. some GM crops are resistant to herbicides, this means farmers can spray their fields to kill weeds without harming the GM crop.
• genetic modification is currently being explored as a way to treat inherited disorders in humans, this is called gene therapy.
• the long term effects of gene therapy are not known. we don't know the potential effects on other genes if we modify one gene.
• genetic engineering

  1. identify the gene we want to transfer
  2. use enzymes to isolate this gene
  3. transfer gene into a small circle of DNA called a plasmid
  4. plasmid transfers DNA from one organism to another, so we call them vectors
  5. the desired gene is transferred into the cells of the target organism.
• for genetic engineering, we always transfer the gene at an early stage in the organisms development e.g. if we were transferring a gene to an animal, we would do this at the early embryo stage, this is to make sure that all of the cells receive the transferred gene, so the organism develops with the characteristic that we want
• asexual reproduction produces genetically identical organisms, these are called clones
• cloning plants has one big advantage, because the clone is genetically identical to the original plant, we know exactly what the clones characteristics will be e.g. colour of the flowers
• a simple way to clone a plant is by taking cuttings. a small piece of the plant is removed and the end is dipped in rooting powder. rooting powder contains plant hormones and this encourages the plant to develop roots.
• by taking cuttings, we produce a genetically identical clone of the started plant. it works really well if we just want a few clones from a plant. however, if we need hundreds of clones, we use tissue culture.
• in tissue culture, we take a plant that we want to clone and we divide the plant into hundreds of tiny pieces. each of these pieces contains a small number of cells. these small groups of cells are then incubated with plant hormones, the plant hormones stimulate the plants to grow and develop into fully-grown clones.
• the conditions that we use for tissue cloning must be fully sterile, this is because we don't want to introduce an microorganisms such as bacteria or fungi. it is extremely useful in commercial plant nurseries, it allows growers to produce thousands of genetically identical plants quickly and cheaply. as well as the fact we can be certain we will get the characteristics wanted because all plants are clones.
• tissue culture is also used to preserve rare species of plants.
• we can clone animals by embryo transplants.

  1. we start with sperm and egg cell from animals with wanted characteristics
  2. fertilisation happens and we allow it to develop into an early stage embryo although the cells must not have started to specialise
  3. we use a glass rod to split this embryo into 2
  4. we then transplant these 2 embryos into host mothers, the embryos will grow and develop and the hosts will give birth to 2 genetically identical animals.
• the big problem with embryo transplants for cloning is that we cannot be certain that the offspring will have the characteristics that we want. we can overcome this problem by using adult cell cloning
• the main benefit of adult cell cloning is that we are cloning from an adult, this means that we know the characteristics that the clone will have.
• for adult cell cloning to clone animals

  1. remove a cell from adult
  2. remove nucleus from cell
  3. take unfertilised egg cell from same species and remove nucleus from egg
  4. now insert nucleus from the original adult body cell into the empty egg cell, now egg cell only contains genetic information from animal we are cloning
  5. give the egg cell an electric shock and it will divide to form an embryo
  6. inserted into womb of host to give birth to clone, the clone won't look like host
• genetic engineering advantages in agriculture include improved growth rates of plants and animals, increased yield, increased food value of crops, crops can be designed to grow in any conditions.