b. Pure smooth green peas are crossed with pure wrinkled yellow peas. What 

 will be the appearance of the hybrid generation? the genetic make-up? (Let 

 capital Y and S represent the dominant yellowness and smoothness respectively, 

 and small y and s represent the recessive greenness and wrinkledness.) Note (1) the 

 appearance of offspring; (2) the kinds of gametes that the hybrid generation will 

 bear. Work out the results of crossing these gametes, using the "checkerboard" or 

 Punnett squares. 



c. Pure dominant strains of tall smooth yellow peas are crossed with short 

 wrinkled green peas. Use the Punnett-squares method to find (1) the appearance 

 of the hybrid generation; (2) the genetic make-up of the hybrid; (3) the possible 

 gamete types produced by these hybrids; (4) the different phenotypes produced; 

 (5) the ratios among the body types in the offspring; and (6) which types will breed 

 true in later generations, and which will break up again. 



d. A child of brown-eyed parents has blue eyes. Show by the use of genetic 

 symbols and a diagram the probable composition of immediate ancestry. 



e. Henry and Susan both have normal hearing. One of Henry's grandparents 

 was a deaf-mute; among Susan's near relatives two first cousins are deaf-mutes. 

 Show by diagram and genetic symbols the possibility that, should Henry and Susan 

 marry, some of their children might be deaf-mutes. 



/. What would be the expected offspring of a mating of a long-haired guinea-pig 

 with a short-haired guinea-pig one of whose parents was long-haired? 



g. A rough-coated black guinea-pig whose mother was smooth-white is mated 

 with a smooth-white animal. Work out the kinds of offspring and the ratios of the 

 various kinds. 



h. A girl of normal vision whose father was color-bHnd marries a color-blind man. 

 Work out the probabilities as to color-blindness among their sons and daughters. 



5 To study the inheritance of traits in fruit flies, cross the wild type with pure 

 cultures showing characters readily distinguishable without a microscope. Such 

 characters as ebony body and vestigial wings illustrate Mendelian inheritance; white 

 eyes and yellow body illustrate sex-linked inheritance. 



In mating, it is essential to use only virgin females. Since adults in a given culture 

 mate within a few hours after emerging from the pupa, use only cultures in which 

 there are no adults over an hour old. To cross, select one male and one virgin female, 

 from etherized cultures.^ Place pair in a prepared bottle containing suitable food.^ 

 After eight to ten days remove these parents so that there is no chance for them to 



^For etherizing, use a bottle the same size as the culture bottles (widemouthed, 8 oz, or half- 

 pint milk bottle); attach a wad of cotton to a cork with a wire. Moisten cotton with ether. Trans- 

 fer flies from culture to bottle; close and etherize one minute. Dump insects on a piece of clean 

 paper and sort with a camel's-hair brush. The females have a slightly wider abdomen than the males 

 and also small lines across the tip of the abdomen; the males, which are smaller, have a black-tipped 

 abdomen. To prevent the growth of mold, use the commercial preparation "Moldex". 



^To make a growing medium, add 100 g of corn meal, f cup of molasses, and 15 g of agar to 

 750 g of boiling water, while stirring. Cook about 10 minutes. Pour into sterilized bottles, about 

 5 in. in each; then insert in each a strip of paper toweling, on which the larvae may crawl to pupate. 

 With a clean medicine-dropper add to each bottle one drop of water in which a bit of yeast cake has 

 been dissolved. 



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