HEREDITY AND VARIATION 227 



588. In Four-o'clock flowers, let R represent the factor for red flower 

 color and W the factor for white. What will be the flower color of the 

 offspring from the following four crosses, in which the parents' genotypes 

 are given: 



RW X RR; WW X RW; RR X WW; RW X RW? 



589. If you wanted to produce Four-o'clock seed all of which would 

 yield pink-flowered plants when sown, how would you do it? 



590. In what respect is a character which behaves like flower color in 

 Four-o'clocks easier to deal with in breeding work than one which behaves 

 hke fruit color in squashes? 



Note. — In the inheritance of fruit shape in summer squash it has been 

 found that the "disc" type is dominant over the "sphere" type (see 

 Fig. 126). 



591. In a cross between a squash plant homozygous for yellow fruit 

 color and disc fruit shape and a plant homozj^gous for white fruit color 

 and sphere fruit shape, what will be the color and shape of the fruit in 

 the Fi? What will these be in the F2? produced by crossing two of 

 these Fi plants together? 



592. If one of the Fi plants in the preceding question is crossed back 

 onto its yellow disc parent, what will be the color and shape of fruit in 

 their offspring? What will these be if the Fi plant is crossed back onto 

 its white sphere parent? 



593. Let D represent the factor for disc fruit-shape and S the factor 

 for sphere. What will be the color and shape of fruit in offspring of the 

 following crosses: 



WW SS X YY DD WY DS X WY SS 



WY DD X YY SS WY DS X YY SS 



WY DS X WY SS WY DS X WY DS 



Note. — In the following six questions, all of which deal with fruit color 

 and shape in the summer squash, the appearance of parents and offspring 

 is stated. Determine in each case the genotypes of the parents. 



594. White disc crossed with yellow sphere gives one-half white disc 

 and one-half white sphere. 



595. White sphere crossed with white sphere gives three-fourths 

 white sphere and one-fourth yellow sphere. 



596. White disc crossed with yellow sphere gives one-fourth white 

 disc, one-fourth white sphere, one-fourth yellow disc, and onc-fourtli 

 yellow sphere. 



