FISH analysis of γ and β gene transcription during erythroid differentiation in culture. Double-label RNA FISH was performed on cultured erythroid cells from healthy individuals and patients with Corfu deletion with gene-specific, intron probes for γ and β primary transcripts. Percentage of total γ and β gene signals are presented for 2, 4, and 6 days after hemoglobinization. ▦ indicates γ transcription; ▪, β transcription. (A) Healthy individual. Note, as cells mature, β transcription progressively increases while γ transcription is reciprocally silenced. (B) Corfu homozygotes A02 and A06. Note, γ versus β levels are stable over the culture period. (C) Corfu heterozygotes A01, A07, A08, A09. (D) γ Versus β transcription for all individuals assayed: 2 healthy subjects N; Corfu heterozygotes A01, A07, A08, A09; Corfu homozygotes A02 and A06, at day 6 after hemoglobinization when β transcription reaches 90% of total in normal cells. Average percentage of γ is indicated for each group of individuals as Av %γ, ie, 100% γ/(γ + β). Note, γ transcription increases with Corfu chromosome copy number.