4. Variation and Inheritance

• Variation is the differences that exist between members of the same species.
• Sexual reproduction increases variation within a species was it combines genes from separate parents.
• There are 2 forms of variation

  • Discrete
  • Continous
• Discrete variation are differences in characteristics controlled by one single gene. This is called single gene inheritance. These characteristics fall into distinct groups
• Examples of discrete variation include

  • Blood group
  • Eye colour
  • Hair colour
  • Skin colour
• Continuous variation is differences in characteristics that are controlled by more than one gene. This is known as polygenic inheritance. These characteristics can be measured and have a range of values.
• Examples of continuous variation include

  • Height
  • Weight
  • Length of limbs
• A genotype is an individuals alleles for a particular characteristic.
• A phenotype is an individuals physical appearance based on the genotype for a particular characteristic.
• An allele is the different form of a gene which produces different phenotypes.
• Alleles determine which form of gene that you have (E.g blue eyes)
• Dominant alleles always produce a certain phenotype. They are represented by a capital letter.
• Recessive alleles will not be shown in the phenotype if a dominant allele is present. They are represented by a lower case letter.
• A homozygous is an individual who has inherited two of the same alleles for a gene.
• Heterozygous means an individual who has inherited two different alleles of a gene.
• Offspring will not always follow the expected phenotype ratio because fertilisation is random.