MENDELIAN INHERITANCE 



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are separated from one another so as to produce germ cells 

 having only one factor green or yellow. This is known as 

 Mendel's principle of segregation. The hybrid ovule containing 

 both factors is said to be heterozygous and the two factors 

 for the same character (here color) are called allelomorphs, 

 one of which is dominant, the other recessive. If only one type 

 of factors is present in an ovule it is said to be homozygous. 



FIG. 95. Example of Mendelian inheritance in which the hybrid (F') is 

 intermediate between the two parents, but showing segregation of the two factors 

 in the germ cells giving in the F 2 generation the proportion of i : 2 : i. The cross 

 is made between white and red races of Mirabilis japala (the "four o'clock"). 

 The hybrid (Fi) is pink, and these when inbred give white, pink, and red flowers 

 in the proportion of i :2 : i (F 2 ). (From Morgan.) 



Now if the hybrid plants are self-fertilized i.e., through union 

 of their own germ cells and if segregation of factors occurs during 

 the formation of these germ cells in both anthers and ovules 

 then the following combinations may occur (Fig. 94). The 

 green-bearing anther may unite with a green-bearing ovule 

 and the result is green (homozygous); or a green-bearing 

 anther may unite with a yellow-bearing ovule and the result 

 is a heterozygous yellow since yellow is dominant. Or a 



