Hereditary Elliptocytosis SPTA1 AD Pedigree

A 24-year-old woman of Mediterranean ancestry presents with lifelong mild hemolytic anemia that has worsened during pregnancy (Hb now 8.5 g/dL from baseline 11 g/dL). She has neonatal jaundice history, intermittent jaundice with viral illnesses, and underwent cholecystectomy at age 22 for pigment gallstones. Her father has hereditary elliptocytosis with splenectomy at age 45, her paternal grandfather had cholelithiasis and lifelong anemia, and her elder sister (age 28) has hereditary elliptocytosis with cholecystectomy at age 20. Her mother is unaffected. Peripheral blood smear shows >30% elliptocytes. Genetic testing reveals a heterozygous SPTA1 mutation. The pedigree pattern shown in the diagram marked **B** demonstrates which inheritance characteristic?