Variation and evolution: Inheritance, variation and evolution: Biology: GCSE (9:1)

• Phenotype


  The observable features of an organism, influenced by an organism's genome and the interaction of the organism with its environment

  
• Variation


  Differences in the characteristics of individuals in a population

  
• Continuous or discontinuous variation


  Variation can be continuous and hold any numerical value on a scale, or can be discontinuous and discrete where variation is categorical

  
• Examples of continuous variation


  An organism's height or weight are examples of continuous variation as they can have any numerical value including all decimal numbers

  
• Examples of discontinuous variation

  An animal's fur colour or a human's blood type or shoe size are examples of discontinuous variation as the data is best organised into distinct categories

  
• Source of variation

  All variants arise from mutations, most of which have no effect on the phenotype, some influence the phenotype and very few actually determine the phenotype

  
• Genetic reshuffling during meiosis


  Genetic information is swapped between chromosomes during meiosis, which can be another source of variation other than mutations

  
• Causes of variation

  Expression of genes that have been inherited, the conditions in which an organism has developed or a combination of genes and the environment

  
• Examples of variation caused by genetic factors

  Blood type, skin or fur colour at birth, eye colour, genetic disorders

  
• Examples of variation caused by the environment

  Scars, language or human modifications such as tattoos or piercings

  
• Examples of genetic and environmental variation

  Weight, height, skin colour, hair colour

  
• Variation in a population


  There is usually extensive genetic variation in the population of a species

  
• Frequency of mutations


  Mutations occur continuously but will very rarely lead to a new phenotype
• Adaptive phenotypes


  If a new phenotype is suited to environmental change it can lead to a relatively rapid change in a species

  
• Evolution


  A change in the inherited characteristics of a population over time through the process of natural selection, can result in speciation

  
• Natural selection


  A process where variants give rise to phenotypes that are best suited to an organism's environment, increasing the chances that the organism will successfully reproduce

  
• Genetic variants


  Changes in DNA as a result of mutation, can sometimes affect the overall phenotype of an organism

  
• Survival of the fittest

  A concept of natural selection, where individuals with adaptive phenotypes are more likely to survive and pass on their genes to their offspring

  
• Offspring


  The young born of an organism, for natural selection to occur any adaptive phenotypes must be heritable by the offspring

  
• Ancestral life forms


  The theory of evolution by natural selection states that all living things are descended from simple life forms that developed more than three billion years ago

  
• Speciation


  An outcome of evolution, where two populations of a species become so different in phenotype they can no longer interbreed to produce fertile offspring