Structure of the "-globin and !-globin genes

As a result of their origin froma common ancestral
gene, all globin genes have a similar structure.
Their coding sequences are arranged in
three exons. Each globin transcription unit includes
nontranslated sequences at the 5' and
the 3' ends (see section on the structure of
eukaryotic genes, p. 50). The lengths of the !-
globin and $-globin exons are similar (e.g., exon
1 of the ! gene has 30 codons; exon 1 of the $
gene has 31 codons), whereas the lengths of the
introns differ.