SCOPE OF GENETICS 17 



in the same condition as they went in at 

 fertilisation. 



As a consequence of these facts it follows 

 that however complex may be the origin of 

 two given parents the composition of the off- 

 spring they can produce is limited. There is 

 only a limited number of types to be made 

 by the possible recombinations of the parental 

 ingredients, and the relative numbers in which 

 each type will be represented are often pre- 

 dicable by very simple arithmetical rules. 



For example, if neither parent possesses 

 a certain factor at all, then none of the off- 

 spring will have it. If either parent has two 

 doses of the factor then all the children will 

 have it ; and if either parent has one dose of 

 the factor and the other has none, then on 

 an average half the family will have it, and 

 half be without it. 



To know whether the parent possesses 



B. 2 



