Concept 4: Genes can change on occasion and the alternative version or allele may control the trait

While genes are stable, they can be altered to encode different genetic information. An alternative form of a gene is called an allele. Genetic variation relies upon alleles. To designate genes and their alleles we often use single letters such as ‘A’ and ‘a’ (Fig. 7).

Figure 7. Changing the coding region of a gene will result in the production of a different protein. This can alter the organism’s traits. (Image by P. Hain)