Bài 3: Ở ruồi giấm, alen A quy định thân xám trội hoàn toàn với alen a quy định thân đen. Cặp alen này nằm trên cặp nhiễm sắc thể số II. Cho các con ruồi cái thân xám giao phối ngẫu nhiên với các con ruồi đực thân đen -> F1 có 75% xám và 25% đen. Cho F1 giao phối ngẫu nhiên -> F2​ a) Giải thích kết quả, viết SĐL từ P đến F1​ b) Số con ruồi giấm thân đen ở F2 chiếm tỉ lệ bao nhiêu?

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