PROBLEM A Hoxv Can Some of the Differences Between 



Parents and Offspring Be Explained? 



"You look just like your uncle." Do you 



look more like a grandparent than like 

 one of your own parents? Perhaps you 

 resemble more closely some aunt, or 

 uncle, or cousin. You may have blond 

 hair and blue eyes and differ from your 

 brother who has dark hair and brown 

 eyes, or dark hair and blue eyes, or 

 blond hair and brown eyes. Again you 

 may have blue eyes although both your 

 parents and your brothers and sisters are 

 brown-eyed; you may be taller than 

 either of your parents. In many ways 

 your characteristics may be different 

 from those of your close relatives. Why 

 is there such variety in members of the 

 same family? Is it all haphazard or are 

 there laws of heredity? Study Figure 410. 



Much experimental work has been 

 done to solve the problems of heredity 

 in other animals and in plants. Let us 

 examine some of this work and learn to 

 apply the results to ourselves. 



Color inheritance in the four-o'clock. 

 The four-o'clock is a plant which re- 

 sembles the more familiar morning glory. 

 How does heredity operate when red- 

 flowered and white-flowered plants are 

 crossed (mated)? To answer the ques- 

 tion the following procedure is used. 

 Pollen from a white flower is transferred 

 by hand to the pistil of a red flower on 



another plant. Sometimes the reverse is 

 done: pollen from a red flower is put on 

 the pistil of a white flower. To make 

 sure there is no accidental pollination, 

 the stamens of the flowers that are to re- 

 ceive the pollen are removed and after 

 the desired pollen has been added the 

 flowers are covered with paper bags. 

 This keeps off other pollen (Fig. 412). 

 Fertilization occurs, the flowers wither, 

 and the fruits and seeds develop under 

 the paper bags. Careful records are kept 

 so that the parentage of every seed is 

 known. The seeds from these fertiliza- 

 tions are planted the next season. When 

 the plants grow up and bloom, their 

 flowers are pink. That probably does not 

 surprise you. 



Then the experiment is continued by 

 crossing those pink-flo\^^ered plants, 

 and a strange thing happens. The off- 

 spring are of three different kinds: some 

 have pink flowers, as you would expect, 

 but others have white flowers and still 

 others red. When the number of plants 

 in the experiment is large, about 25% of 

 the offspring are white-flowered, about 

 50% are pink-flowered, and about 25% 

 are red-flowered. This is in the ratio of 

 1:2: 1. The experiment can be continued. 

 If the red-flowered grandchildren are 

 crossed with red-flowered grandchildren 



