Mouse haemoglobin β chains. Sequence data on embryonic γ chain and genetic linkage of the γ-chain locus to the adult β-chain locus Hbb

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Abstract
Embryonic haemoglobin y-chain types were determined by starch-gel electrophoresis for inbred Mus musculus strains Sec/ReJ and Au/SsJ (with Hbbs and Hbbp adult β-chain alleles respectively) and for random-bred HA/ICR (Swiss) mice, which had been selected to be homozygous for the adult Hbbd β-chain allele. The strain with the Hbbs allele had y1 embryonic β chain and the strain with the Hbbd allele had y2. The strain with the Hbbp allele also had y2 chain. A breeding study showed that the maximum recombination frequency between the Hbb locus and the y-chain locus is 5.4% at the 95% confidence level. Embryonic y2 chain was sequenced for 39 positions from the N-terminus with an Edman-Begg sequenator. Some tryptic-peptide composition data were obtained on both y1 and y2 chains. No amino acid substitutions between y1 and y2 chains were found in the 40 positions for which there are common data on the two chains. y2 and adult β chains are different in 12 of the first 21 positions, but show considerable similarity thereafter. It is suggested that homologous but unequal crossing-over between y-chain and adult β-chain loci could have given rise to the adult β-chain allele Hbbd, which produces structurally different major and minor β chains from two closely linked genes.