Bạn đang quan tâm đến sự di truyền trong một quần thể rắn chuông. Hai đặc điểm mà bạn quan tâm là hình dáng hoa văn và màu sắc hoa văn. Hình dạng có thể là tròn hoặc kim cương và màu sắc có thể có màu đỏ hoặc đen. Bạn có thể xác định rằng hình dạng được qui định bởi gen A trong khi màu sắc được xác định bởi gen B. Bạn cũng xác định rằng kim cương, đen là những tính trạng trội. Bạn cho lai một con rắn kim cương màu đen với một con rắn hình tròn màu đỏ. Con rắn kim cương đen là dị hợp cho cả hai gen. Tỷ lệ cá thể có kiểu hình đen tròn trong các con F1 là bao nhiêu?

A. 1/4                         

B. 1/8                      

C. 1/16                    

D. 3/4

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.

Very few people in the modern world obtain their food supply by hunting and gathering in the natural environment surrounding their homes. This method of harvesting from nature’s provision is the oldest known subsistence strategy and has been practised for at least the last two million years. It was, indeed, the only way to obtain food until rudimentary farming and the domestication of wild animals were introduced about 10,000 years ago.

Because hunter-gatherers have fared poorly in comparison with their agricultural cousins, their numbers have dwindled, and they have been forced to live in marginal environments, such as deserts and arctic wastelands. In higher latitudes, the shorter growing seasons have restricted the availability of plant life. Such conditions have caused a greater dependence on hunting, and on fishing along the coasts and waterways. The abundance of vegetation in the lower latitudes of the tropics, on the other hand, has provided a greater opportunity for gathering a variety of plants. In short, the environmental differences have restricted the diet and have limited possibilities for the development of subsistence societies.

Contemporary hunter-gatherers may help us understand our prehistoric ancestors. We know from the observation of modern hunter-gatherers in both Africa and Alaska that a society based on hunting and gathering must be very mobile. While the entire community camps in a central location, a smaller party harvests the food within a reasonable distance from the camp. When the food in the area has become exhausted, the community moves on to exploit another site. We also notice seasonal migration patterns evolving for most hunter-gatherers, along with a strict division of labor between the sexes. These patterns of behavior may be similar to those practised by mankind during the Paleolithic Period.

In the lower latitudes of the tropics, hunter-gatherers ______.

A. have better food gathering from nature   

B. can free themselves from hunting

C. harvest shorter seasonal crops       

D. live along the coasts and waterways for fishing