3.1  Genes

big ninja

Essential Idea:

Every living organism inherits 

a blueprint for life from its parents


  • A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic
  • A gene occupies a specific position on a chromosome
  • The various specific forms of a gene are alleles
  • Alleles differ from each other by one or only a few bases
  • New alleles are formed by mutation
  • The genome is the whole of the genetic information of an organism
  • The entire base sequence of human genes was sequenced in the Human Genome Project


  • The causes of sickle cell anaemia, including a base substitution mutation, a change to the base sequence of mRNA trancribed from it and a change to the sequence of a polypeptide in haemoglobin
  • Comparison of the number of genes in humans with other species


  • Use of a database to determine differences in the base sequence of a gene in two species