双倍体染色体交换 Centromere Centromeres Homolog Homologous pair Homolog Chromatids Tetrad Crossover point (chiasma) (b) Figure 24-26 Crossing over.(a)The homologous chromosomes of a grasshopper are shown during (a) 24m prophase I of meiosis.Multiple points of joining (chiasmata)are evident between the two homolo-双倍体染色体交换