Bj, Bg, Bg. — First, second and third backcrosses respectively. 



B-indolylacetic Acid. — A plant growth stimulant present in 

 urine; heteroauxin. 



Backcross. — A cross between a hybrid and either of its 

 parents, or between a heterozygote and a homozygous reces- 

 sive. 



Backcross Parent. — That parent of a hybrid with which it 

 is again crossed or with which it is repeatedly crossed; re- 

 current parent. 



Backcross Ratios. — The proportion of heterozygotes to bot- 

 tom recessives expected in a backcross is given by calculating 

 2" where n is the number of factors involved, e.g. with 2 

 factors 2ii = 4 and the expected ratio is 3:1 with 3 factors 

 2^1 = 8 and the expected ratio is 7:1, etc. 



Background Adaptation. — The agreement between the colour 

 and appearance of an organism and the general appearance of 

 the environment in which it lives. 



Back-mutation. — The mutation of a mutant gene back to its 

 original state. 



Back-Pollinating. — Backcrossing. See Backcross. 



Baculif orm. — Of chromosomes : rod-shaped. 



Balance. — A state of harmonious adjustment of the interaction 

 of the genes or chromosomes of an organism so that its devel- 

 opment is normal. 0pp. Unbalance. 



Balance, Secondary. — A new balance derived by change in 

 the proportion of genes, as in a secondary polyploid, from an 

 old balance and capable of competing with it (Darlington 

 & Moffett). 



Balanced Lethals. — Closely linked lethal factors located in 

 chromosomes of opposite gametes so that crossing over is 

 infrequent and the factors remain in repulsion. 



Balanced Polymorphism. — See under Polymorphism. 



Balbiani-type Chromosomes. — Giant chromosomes whether 

 occurring in salivary glands or elsewhere, of. Salivary Gland 

 Chromosomes. 



