284 EVOLUTION, GENETICS, AND EUGENICS 



To bring the facts of sex-linked heredity sharply into focus by 

 way of summary, let us quote from D. F. Jones a genetic formulation 

 of the whole matter: 



"Rules for sex-linked inheritance. — From this series of facts the 

 following rules governing the transmission of sex-linked characters 

 can be deduced. 



"1. When the homozygous sex transmits the dominant factor, all 

 of the offspring in the first generation exhibit the dominant character 

 and the second generation is composed of three dominants to one reces- 

 sive, the latter having the same sex as the recessive grandparent. 



"2. When the homozygous sex transmits the recessive factor, both 

 dominant and recessive characters are exhibited in the first generation, 

 but exclusively upon the opposite sexes, and in the second generation 

 both sexes show the sex-linked characters in equal numbers." 



