440 



Plant-Breeding 



Phenotypes (visible types) (2 n ) = 3 TT ; 1 tt. 

 Genotypes (actual types) (3 n ) = 1 TT ; 2 Tt ; 1 . 



Problem 2. - 



Heterozygous Tall (TO X homozygous dwarf (tt). 



Whenever a plant which is already heterozygous is used as a 

 parent, its gametes will become segregated during their formation, 

 and when the crossing takes place more than one kind of progeny 

 will be produced. In this case the female parent will produce 

 two kinds of egg cells, namely, tall and dwarf. 



Graphically, this cross may be represented as follows : 



EGG CELLS 



The male parent is pure dwarf, therefore all of the pollen grains 

 will represent dwarfness only. 



Phenotypes = 2 Tt; 2 tt. 

 Genotypes = 2 Tt ; 2 tt. 



If the female parent were crossed with a homozygous tall 

 instead of a dwarf, the visible types the first year after crossing 

 would all appear the same (tall) instead of two kinds as above. 

 There would be 



Phenotypes = 4 TT. 



Genotypes = 2 TT 7 ; 2 Tt. 



