ABSTRACT
Only a very small number of the mutations occurring in a multicellular organism are passed on to the next generation. To be inherited in this way a mutation must occur in a sex cell, evade the cell’s repair enzymes, and be passed on to a gamete that participates in formation of a fertilized egg cell (Figure 17.1). Working out how many such mutations occur per generation is very diffi cult, but it is thought that each human being possesses over 100 new mutations that are absent from the somatic cells of their mother and father, and which therefore arose in the sex cells of those two parents prior to the individual’s conception. This might sound like a minute degree of change, bearing in mind that the human genome contains 3200 Mb and only 4% of this comprises coding DNA. Most, if not all, of those 100 unique mutations possessed by an individual will therefore be in intergenic regions, but occasionally one will occur in the coding part of a gene, creating a new allele.
