Variation

• Variation - differences between individuals of the same species
• Phenotypic variation - the difference in features between individuals of the same species

  • Some of these differences are caused by differences in genes, which is genetic variation
• Phenotypic variation can be divided into two types depending on how you are able to group the measurements:

  • Continuous Variation 
  • Discontinuous Variation
• Continuous Variation - when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale

  • e.g. height, mass, finger length etc. where there can be many ‘inbetween’ groups
• Discontinuous Variation - when there are distinct differences for a characteristic

  • e.g. people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not - there are no ‘inbetweens’
• Continuous variation gives smooth bell curves (a result of all the small degrees of difference)

  
• Discontinuous variation gives a ‘step – like’ shape

  
• Phenotypic variation can be caused in two main ways:

  • It can be genetic - controlled entirely by genes
  • It can be environmental - caused entirely by the environment in which the organism lives
• Examples of genetic variation in humans:

  • blood group
  • eye colour
  • gender
  • ability to roll tongue
  • whether ear lobes are free or fixed
• Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle

  • ‘environmental’ means ‘outside of the organism’ and so can include factors like climate, diet, culture, lifestyle and accidents during lifetime
• Examples of environmental factors:

  • An accident may lead to scarring on the body
  • Eating too much and not leading an active lifestyle will cause weight gain
  • Being raised in a certain country will cause you to speak a certain language with a certain accent
  • A plant in the shade of a big tree will grow taller to reach more light
• Discontinuous variation is usually caused by genetic variation alone
• Continuous features often vary because of a combination of genetic and environmental causes:

  • tall parents will pass genes to their children for height
  • their children have the genetic potential to also be tall
  • however if their diet is poor then they will not grow very well
  • therefore their environment also has an impact on their height
• Although genes decide what characteristics we inherit, the surrounding environment will affect how these inherited characteristics develop
• Mutations are genetic changes

  • Most mutations have no effect on the phenotype as the protein that a mutated gene produces may work just as well as the protein from the non-mutated gene
• Rarely, mutations lead to the development of new alleles and so new phenotypes and if they do, most have a small effect on the organism

  • the new allele sometimes gives the individual a survival advantage over other members of the species
• Example of mutations having effect on organisms:

  • A bird develops a mutation leading to a change in feather colours
  • Makes it more attractive to birds of the opposite sex
  • Causes the bird to breed more frequently and have more chances of passing on the mutated phenotype to the next generation
• Mutations can also lead to harmful changes that can have dramatic effects on the organism

  • e.g. sickle cell anaemia in humans
• Mutations happen spontaneously and continuously but their frequency can be increased by exposure:

  • Ionising radiation (e.g. gamma rays and X - rays) - which can damage bonds and cause changes in base sequences
  • Some non-ionising radiation (e.g. ultra-violet) - can also damage bonds and cause changes in base sequences
  • Certain types of chemicals - for example chemicals such as tar in tobacco
• Increased rates of mutation can cause cells to become cancerous
• Mutations are random genetic changes to the base sequence of DNA
• Mutations

  • New alleles form through random changes to DNA
• Meiosis

  • New allele combinations form through segregation
• Random mating

  • Partnerships form for sexual reproduction
• Random fertilisation

  • Sperm and egg combinations occur during sexual reproduction
• Phenotypic variation - variation of phenotype
• Genetic variation - the genetic makeup of an organism in terms of the alleles present
• Continuous variation - a range og phenotypes between 2 extremes e.g. height in humans
• Discontinuous variation - a limited number of phenotypes
• New alleles are formed through a change in the base sequence
• Mutation - genetic change
• Genetic mutation - a genetic change in the base
• Define discontinuous variation


  Discontinuous variation is variation that fits into a discrete set of categories
• The process a farmer could use to breed __(dominant trait)___


  • Use selective breeding
  • Breed / cross / mate two with the dominant trait
  • Select the offspring with the dominant trait and breed them again
  • Should be done over many/several generations
  • To ensure/create a population that are homozygous dominant
• Continuous Variation: results in a range of phenotypes between two extremes; examples include body length and body mass
• Discontinuous Variation: results in a limited number of phenotypes with no intermediates (e.g. ABO blood groups, seed shape in peas and seed colour in peas)

  • It is usually caused by genes only, and genes and the environment cause continuous variation.
• You must be able to investigate and describe examples of continuous and discontinuous variation

  
• Mutation - a genetic change.
• Mutation is the way in which new alleles are formed
• Gene Mutation- a change in the base sequence of DNA