HBB (source code)
= HBB
{c}
\b[HBB] is the human <gene> encoding <beta-globin>, a component of <hemoglobin A>. It lies in the beta-like globin region of <chromosome> 11. The usual adult <hemoglobin A> assembly contains two <alpha-globin> and two <beta-globin> chains.<Human globin gene records in NCBI Gene>[Human HBB, Gene3043, RefSeq summary; human alpha-chain annotations]{ref}
The locus is distinct from an <allele> at that locus. A sequence variant can change the encoded chain, alter its production or have another molecular consequence depending on its position and effect. The word <HBB> alone does not specify a particular variant or establish a clinical phenotype.
A historically important experiment used this locus as a target for enzymatic <DNA> amplification. A 1985 primary study amplified beta-globin genomic sequences and used restriction-site analysis to distinguish sequence information relevant to <sickle cell disease>.<Enzymatic amplification of beta-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia by R. K. Saiki and others>[Abstract, target amplification and restriction-site readout]{ref} Increasing the amount of a selected <DNA> region made analysis easier; the sequence-sensitive readout supplied the distinguishing information. Amplification alone did not make all possible <HBB> alleles identical or identify them without a readout.
An original assembly-count example links gene products to the <protein> complex. If a hypothetical pool contains 100 usable alpha chains and 80 usable beta chains, and only $\alpha_2\beta_2$ tetramers are allowed, the maximum assembled count is $\min(100/2,80/2)=40$. Twenty alpha chains remain outside that counted product. Real synthesis and degradation add further processes, but the example explains why a chain-producing <gene> and total assembled <hemoglobin> are different quantities.
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