A single gene disorder - Research Paper Example

It has a wide prevalence worldwide especially in Africa where the occurrence is in about 1 in 100 individuals (Genetics, 2000; Online Mendelian Inheritance in Man). Single-gene disorders generally arise due to mutations or changes in a single gene of the genome. Subsequent changes in the protein product of that gene give rise to a disorder. These disorders could be inherited due to an autosomal dominant or recessive gene or a X-linked inheritance. Every individual acquires two copies of a gene, one form each parents and in the dominant inheritance the disorder occurs if one copy of the gene is defective and in the recessive inheritance it exhibits only if both the copies of the gene are defective.

In the case of X-linked disorder, the defective gene is present in the X chromosome and the disease manifest most commonly in males as they only have a single copy of the X chromosome (Human Genome Project Information, 2008). One such single-gene disorder is sickle cell disease which occurs due to a single point mutation in the gene coding for the hemoglobin protein. It has an autosomal recessive mode of inheritance. Hemoglobin, the most important protein of the red blood cell, is made up of four globin subunits, two α and two β subunits, which are coded by their respective genes.

Every individual inherits two copies of a gene from each parent which are referred to as alleles. The normal allele for the β globin subunit is referred to as allele A and the mutated allele as S. A normal individual possessing AA alleles will have a normal hemoglobin moiety, while individuals carrying one A and one S allele will produce both normal and abnormal hemoglobin molecules, as both the A and S allele are co-dominant, and are referred to as carriers of sickle cell trait who are generally healthy but may suffer from sickle cell symptoms under conditions of