332 HEREDITY 



tall and those of the short will be short. Diagraras similar to 

 Punnett's (on page 328) may be worked out. Use a capital 

 " T " for tallness and small *' t " (small letter indicates the lack of 

 dominant character) for dwarf ness. The gametes at the top of the 

 squares are the sperms and those at the side are the eggs. The 

 combinations in the squares will show the meeting of the chromo- 

 somes in the fertilized eggs. 



Formulae. (1) T X T = TT. 



(2) tXt = tt. 



When the dominant character is present in one parent only, then 

 the offspring will have only a single contribution of the gene. The 

 offspring will appear dominant but will be a hybrid. 



Formula. T X t = Tt. 



What happens when hybrids are mated? It is believed that 

 during maturation the contrasting factors of hybrids go into the 

 separate eggs or sperms. Thus, the male primary sex cell will 

 be hybrid, but one half of the sperm cells will carry the recessive 

 factor and one half the dominant. Likewise, half the eggs will 

 carry a dominant factor and half the recessive. In other words, 

 the mature germ cells are always pure as regards any one 

 character. The individual may be a hybrid but the gametes are 

 never hvbrid. 



When these gametes of hybrid parents join, the law of proba- 

 bility shows that the following combinations are possible. 



T — ^T 

 Formula. X =TT, Tt, tT, tt 



When a hybrid is crossed with a dominant, the gametes of the 

 hybrid will be half dominant and half recessive, while the gametes 

 of the dominant parent will all carry the dominant gene. The 

 following combinations are possible. 



T — >T 

 Formula. \^ =TT, TT, tT, tT 



t^^T 



