360 LAW OF INDEPENDENT ASSOCIATION 



independently of one another, but also they recombme in 

 F;j independently of one another. 



The Mechanism of Reassortment is the same as 

 that involved in the segregation of a single pair of genes. 

 It merely adds to the segregation of one pair the simulta- 

 neous segregation of one or more additional pairs. The 

 diagrams show how this is accomplished. 



Parents: 



Gametes: 



me Hybrid: 



Nuclei of 

 the tall white 

 and the short 

 purple parent 



Reduction division and 



segregation of two pairs 



of chromosomes. 



Fia. 100 is a diagram of reduction divisions of the tall white and 

 short purple parents, etc. 



The Chromosomes of the Tall Purple Hybrid. — 

 The pea has seven pairs of chromosomes, only two of 

 which are concerned with the present experiment. All 

 further mention of the other five pairs will therefore be 

 omitted. When the reduction division occurs each pair 

 segregates (as shown in the diagram) so that the gametes 

 receive only one member of each pair. The gamete of 

 the tall white thus receives one chromosome containing 

 the " Tall " gene T and another containing the " white " 

 gene p. Similarly the gamete of the short purple receives 

 one chromosome with the " short " gene t, another with 

 the " Purple " gene P. These are the only kinds of 

 gametes these parents can form. Since there is only one 

 kind of gamete formed by each parent only one combina- 

 tion can result: viz., that shown in the diagram for the 

 nucleus of the hybrid. In one pair one chromosome has 

 the gene T and its mate the gene t. In the other pair, 



