CHROMOSOMES AND GENES 



53 



this slip furnishes an opportunity to study the changes 

 that take place in sex-linked inheritance. The most com- 

 mon disturbance is due to the failure of the two X's in 

 the female to disjoin at one of the maturation divisions. 

 The process is called non-disjunction. If an egg that has 



disjunction 



Non-disjunc+ion 



Fig. 34. 



Diagram to show the fertilization of an '"* allached X^^-er XX-egg 

 by a Y-sperm, producing a non-disjunctional XXY female. 



retained its two X-chromosomes (and one of each of the 

 other chromosomes, Fig. 34) is fertilized by a Y-sperm, 

 an individual is produced — a female — that has two X's 

 and a Y. When the eggs of the XXY female mature, that 

 is, when the reduction of the chromosomes takes place, 

 some irregularity is introduced in the distribution of the 



