PROBLEM 2. Dif[ere?ices Between Fare?its and Offspring ^.75 



expect red, white, and pink offspring when vou cross two pink plants. 

 If there is a very large number of offspring what ratio may you 

 expect? 



5. Is the offspring of a pure black and a pure white guinea pig pure or 

 hybrid? How does the result of this cross differ from the result of a 

 red and a white four-o'clock cross? Explain the difference between 

 blending inheritance and dominance. 



6. Name three contrasting characters with which Mendel experimented? 

 How did he obtain pure plants to use as parents? What is meant by 

 the expression "breed true"? 



7. Illustrate by diagram what Aiendel meant by the law of segregation. 

 Nowadays, how is the law stated? Which plants and animals have 

 been used particularly for experimental purposes? 



8. List four good reasons why the fruit fly is a good animal for genetic 

 experiments. 



9. (Optional) Explain, by giving an example, what is meant by Mendel's 

 law of unit characters. 



10. (Optiojial) How many kinds of plants differing in appearance from 

 one another can be expected when you cross two identical dihybrids? 



11. (Optional) Under which circumstances do genes fail to assort inde- 

 pendently of one another? In all Mendel's experiments with the gar- 

 den pea did he find linkage, independent assortment, or both? 



12. (Optional) How do the chromosomes in a man's body cells differ 

 from those in a woman's cells? 



13. (Optional) Give two examples of sex-linked characters. Is the gene 

 responsible for the abnormal condition a dominant or a recessive in 

 each case? 



14. State six important generalizations arrived at from a study of this 

 problem. 



Exercises 



1. Draw (diagrammatically) a four-o'clock plant with red flowers (use 

 crayons). Draw one with white flowers. Below, draw their offspring. 

 Imagine that two of these are crossed. Then show what types of grand- 

 children might be expected. 



2. Make diagrams using rectangles for organisms and circles for gametes 

 to illustrate as far as the F^ the result of crossing a pure red with a pure 

 white four-o'clock. 



3. To demonstrate the ratio of the offspring of a hybrid cross. Put 200 

 red beans and 200 white beans into a jar. Imagine that each bean represents 

 an egg formed by a hybrid pink blossom. The red bean (egg) has a gene 

 for red-flower color. (Do not get the impression that the egg would in 

 reality be red.) The white bean (egg) carries a gene for whiteness. Why 

 do you have the same number of red and white beans in the jar? Set up 

 another jar like it; in this case imagine that each bean represents a sperm. 



