Motttfr T»th«r' 



[? 1 father defeetW*. Mother no* 



No offspring defootiv* 



Half tha sons defeetlv* 



f3 



Balf the Bon« and half tha 

 dau^ters defective 



All offspring defective 



All flontf defective 

 Daughters not 



Figure 25. Diagram to illustrate the descent for successive genera- 

 tions of a defective X-chromosome derived from the original male 

 parent, when there is inbreeding among the descendants, with the 

 various types of results produced. The defective X-chromosome is 

 represented in outline, while the normal X-chromosomes, derived 

 from the mother, are represented in solid black. (The Y-chromo- 

 some, found in males only, is represented as smaller and hooked.) 

 The horizontal rows of outlines show the chromosomal conditions 

 in the individuals of successive generations (Fi to F4) derived from 

 the two parents at the top. Females (with two X-chromosomes) are 

 at the left; males (with X and Y) are at the right. The arrows indi- 

 cate the parentage of the successive generations. The defective X pro- 

 duces a recessive personal defect, so that individuals containing only 

 the defective X (with or without Y) are personally defective. All 

 individuals containing a normal X (black) are normal. 



88 



