STRUCTURAL CHANGE 



cliange can give homozygotes for the two new cliromosome types. 

 These are still balanced. Indeed all these primary structural changes, 

 apart from simple loss, which eliminates itself, merely rearrange the 

 materials in the chromosomes. New chromosomes are created but 

 there is no change in their aggregate content. But by recombination 

 with normal homologues at meiosis secondary changes arise. Our 

 translocation will give heterozygotes and homozygotes for ac and 

 ^t^ which will be deficient in the segment h and meet the fate of 

 deficiencies. And it will give heterozygotes and homozygotes for 

 abc and dbef which will have a duplication o£h. Such individuals will 

 usually be viable but they will be different from the original type. 

 Again, by translocation within itself abcde can become adbce. On 

 crossing-over with the normal homologue in the heteroz)'gote, such 

 a changed chromosome will likewise give deficient (ade) and dupli- 

 cated (abcdbce) progeny from crossing-over in d, and similarly abce 

 and adbcde from crossing-over in be. 



TABLE 10 



THE CLASSIFICATION OF THE TWO ORDERS OF 

 CHROMOSOME CHANGE IN THEIR PRIMARY AND, 

 FOLLOWING RECOMBINATION, SECONDARY CON- 

 DITIONS 



103 



