Final answer:
There are approximately 300 different alleles of the human alpha and beta globin genes worldwide, causing diverse hemoglobin disorders such as thalassemia and sickle cell anemia due to various mutations.
Step-by-step explanation:
Approximately 300 different alleles of the human alpha and beta globin genes have been documented worldwide. These variations are responsible for the diverse hemoglobinopathies observed, such as sickle cell anemia and thalassemias. The beta-globin gene, for instance, can have mutations at different sites, contributing to conditions like beta-thalassemia due to a decreased rate of globin synthesis.
Specifically, beta-thalassemia can be attributed to mutations at eight or more sites within the beta-globin gene. In general, the human globin gene family includes alpha globin genes (designated alpha 1 and 2) and beta globin genes (beta 1 and 2), each binding to a heme molecule containing iron.
Normal adult hemoglobin (HbA) contains two alpha and two beta chains, whereas other variants, such as HbA2 and HbF, involve combinations of alpha with delta and gamma chains, respectively.
Because there are multiple alleles for each gene, genetic heterogeneity accounts for the array of observed phenotypes in the population.
The alpha-globin gene cluster is also complex, but mutations that drastically reduce the rate of synthesis of the alpha chains, leading to alpha-thalassemia, are less common due to the presence of two gene pairs encoding for alpha chains.