Kiểu gen nhân/ Kiểu gen TBC/ Kiểu hình: - rf rf / S bất dục / Phấn hư - rf rf / N hữu dục / Phấn tốt - Rf Rf hoặc Rf rf / N hữu dục / Phấn tốt - Rf Rf hoặc Rf rf / S bất dục / Phấn tốt A, B, C, D là những dòng thuần Bắp lai đơn có công thức: AxB và CxD Bắp lai kép có công thức: (AxB) x (CxD) Kiểu gen của bắp lai đơn và lai kép như thế nào để khi sản xuất hạt giống khỏi phải khử đực và khi trồng sản xuất khỏi phải bổ sung phấn

Our planet has experienced five major extinctions in the four billion year history of life. the first, 450 million years ago, occurred shortly after the evolution of the first land-based plants and 100 million years after the cambrian explosion. the second extinction occurred 350 million years ago, causing the formation of coal forests. next earth experienced two mass extinctions during the triassic period, between 250 and 200 million years ago. the fifth mass extinction occurred 65 million years ago, ending the reptilian dominance of the earth. according to richard leakey, the sixth mass extinction is happening right now. leakey suggests that we, the human race, are the cause. each year, at our hand, approximately 50,000 species vanish from earth. he believes that man is destroying earth at a rate comparable with the impact of a giant asteroid. leakey's statistics indicate that 50% of earth's species will become extinct within the next 100 years assuming leakey's hypothesis of a sixth mass extinction to be true, how will we expect the model to change? a) a sharp spike in the graph approximately 100 million years from now b) a dip in the graph, followed by a sharp spike about 100 million years from now c) a sharp spike in the graph immediately following the "0" location of the x axis d) a plateau following the "0" mark on the x axis, followed by a gradual rise to a new peak