Which of the following statements concerning abnormalities of the haemoglobin molecule is true? 1) Alpha thalassaemia is due to a deficiency of beta-chain production 2) HbS is caused by a single base mutation on the beta-chain 3) genes for the alpha and beta chains are located on the same chromosome 4) in thalassaemia persistance of HbF is an adverse prognostic sign 5) oliguneoclitide probes may assist in the diagnosis of haemoglobinopathies