Monohybrids 



81 



organisms in which only one pair of alleles is being studied are 

 called monohybrids. Some interesting characters in maize de- 

 termined by single genes are shown in Fig. 26, and a striking 

 structural character in Shepherd's-purse in Fig. 27. 



Fig. 26. Some interesting inherited types in Zea mays. Left to right, 

 pop, flint, sweet, pod, and dent. The sweet and floury types appear to 

 differ from flint by single recessive genes, and the pod type by a dominant, 

 but popcorn and dent probably differ by a number of interacting genes. 

 (Photograph by Dr. W. Brooks Hamilton.) 



If a fly is homozygous for curved wings, it will have two c 

 genes, one in each homologue. Since the two homologues separate 

 at meiosis the two c genes must separate, or segregate, also. Since 

 each gamete has only one member of chromosome II, it can have 

 only one c gene; and since the fly is homozygous, all its gametes 

 must be alike. Similarly, in flies homozvgous for the dominant 

 allele, all the gametes must have gene C and must have only one 



