Variation and inheritance

• There are two types of variation

  1. Discrete variation which is controlled by a single gene
  2. Continuous variation which is controlled by several genes (polygenic inheritance)
• Gene is a section of DNA which codes for one protein

  
  

  Allele are different forms of the same gene
• Phenotype is the physical description of a characteristic

  
  

  Genotype is the description of the genes using letters to represent it
• Dominant alleles are dominant and are expressed if you inherit one copy to have this characteristic

  
  

  Recessive alleles are often masked by the dominant alleles and you would need two copies of the alleles to express the characteristic
• Homozygous is if you inherit two of the alleles

  Heterozygous is when you inherit 2 different alleles, one is dominant and the other is recessive
• Phenotypic ratios are not always achieved because

  • fertilisation is a random process
  • sample size may be dependent, if the sample is too small then the ratio may not be shown