<prompt> Red bone marrow is involved in erythropoiesis from3 week to 3 months intra uterine3 months to 5 months Intrauterine5 months IU5 months  <response>: Erythropoiesis:Intra uterine Life:3 wk to 3 month Yolk sac3 month to 5 month Liver spleen 5 Month Red bone marrow Birth to 20 yrs Flat long bones 20 yrs Flat bone 