What is a genotype?

A genotype is an individual’s collection of genes. The genotype of a particular gene, like the gene for beta-globin, refers to the particular mutation a patient has in that gene. For a disease like transfusion-dependent beta-thalassemia, there are many different mutations (dozens or even hundreds) which can cause problems in the beta-globin gene. An individual patient with beta-thalassemia will only have one or two mutations in the beta-globin gene — these mutations are their genotype.