Mutations affect metabolic pathway

• Spontaneous (random) mutations can occur in genes controlling the metabolic pathways. 
• The mutation can stop the metabolic pathway from working if no enzyme is made due to the mutation or the enzyme is non-functional. This can have mild or lethal effects.
• Effect of mutation also depends if the gene producing enzyme is dominant or recessive. If recessive, an individual must inherit two recessive alleles before the pathway is affected. However if the lack of enzyme is caused by a dominant allele, only one has to be inherited. eg metabolic pathway making phenylalanine, recessive mutations in genes that code for 5 enzymes produce 5 rare genetic disorders. The genetic disorders include albinism where the pigment melanin is not formed and alkaptonuria which can cause arthiritis.