20 SOUTHERN PORK PRODUCTION 



matter of fact it has never proven to have any important 

 commercial value. In the past we have always con- 

 sidered that the crossing of two distinct characteristics 

 results in an intermediate character. This may occur in 

 the iirst generation, but if the characters are what have 

 been referred to as unit characters and Mendelizc, some- 

 thing very strange happens, for instead of being an inter- 

 mediate type it will resemble more or less one of the two 

 original characters, and that character or type which it 

 resembles most is referred to as the dominant character. 

 These first crosses are called hybrids, so far as the par- 

 ticular character being studied is concerned. If two 

 hybrids are crossed the characters ma_v Mendelize, or 

 break up, and all of the offspring do not have the same 

 characters, for while about half will resemble their 

 parents, the other half will resemble their grandparents, 

 giving a numerical proportion of 1:2:1 so far as the 

 characters are concerned. This ratio is the Mendelian 

 proportion stated in its simplest form. 



Unit characters. — The number of different characters 

 that are susceptible to Mendel's Law is unknown. New 

 ones are continually being worked out and added to the 

 list. It is assumed that most characters that do not 

 Mendelize are composed in reality of several separate 

 characters, which makes it impossible to study the segre- 

 gation of the several unit characteristics of the offspring. 

 Since each character that ]\Iendelizes is a unit, and since 

 no further division of the character is possible, the char- 

 acter is referred to as a unit character. A great many 

 characteristics have been proven to be unit characters, 

 inherited according to the laws discovered by Mendel. 



Breeding the best to the best. — Since swine improve- 

 ment first began, the principle which has led to the 



