because only one of the two x-chromosomes is active in xx somatic cells , a female heterozygous at the x-linked phosphoglycerate kinase ( pgk-1 ) locus for the usual pgk-1b gene and the variant pgk-1a has two populations of cells , in the cells of one population , pgk-1b is active and b-type enzyme is synthesized , whereas in cells of the other population , a-type enzyme is produced .
C1708726
locus
C0007634
cells