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    So the gene for beta-globulin is HbA, in a person with sickle cell trait, does this come in 2 alleles, the normal allele and the allele with the SNP causing sickle cell disease (which codes for HbS)?
    Thanks.
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    Yes, there are two alleles: HbA and HbS.
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    The genetic transmission of sickle cell disease is of the autosomal recessive type, i.e. the actual disease occurs only if both alleles are abnormal HbS. In sickle cell trait, only one allele is HbS, and this cannot "dominate" the other normal allele, HbA, as the former is recessive (not dominant).

    The "patient" with sickle cell trait does not have his/her haemoglobin with the abnormal amino acid valine instead of glutamic acid at position 6, so he/she has NO symptoms of sickle cell disease.
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    (Original post by macpatelgh)
    The genetic transmission of sickle cell disease is of the autosomal recessive type, i.e. the actual disease occurs only if both alleles are abnormal HbS. In sickle cell trait, only one allele is HbS, and this cannot "dominate" the other normal allele, HbA, as the former is recessive (not dominant).

    The "patient" with sickle cell trait does not have his/her haemoglobin with the abnormal amino acid valine instead of glutamic acid at position 6, so he/she has NO symptoms of sickle cell disease.
    That is incorrect. The HbS allele is not recessive with respect to the HbA allele - it is codominant. Hence, an individual who is heterozygous will produce both normal and mutant haemoglobin. Those who are heterozygous are said to have sickle cell trait. Their symptoms are not as severe as those with sickle cell disease.
 
 
 
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