MENDELIAN LAW OF UNIT CHARACTERS 



329 



of characters. This makes it possible to secure various combina- 

 tions of characters not associated in the original pure stocks. For 

 example, tallness is dominant to shortness, and yellow seed coat 

 is dominant to green seed coat in peas. If a tall, green seed plant 

 is crossed with a short, yellow seed plant, the offspring will all be 

 tall with yellow seeds. Dominants conceal recessives. The fact 

 that each parent had a dominant and a recessive trait does not 

 interfere with the laws of heredity which state that the dominant 

 traits conceal the recessive traits and each pair of characters be- 

 haves independently. New combinations of characters are thus 

 set up in the offspring. Offspring do not resemble either parent 

 in all characters. 



Mendel worked eight years on his garden peas and was able, in 

 1859, to present his results. At that time everybody was excited 

 about Darwin's work. Few, in fact, none, had time for Mendel. 



Pi 



'-^'"'- 



"T' 



In this breeding experiment, pigmentation and quality of hair of guinea pigs are the factors 

 involved. R represents rough hair, r smooth hair ; B denotes black color and b white color or 

 absence of black. The circles show the genes carried by body cells and matured germ cells. 

 An animal of the Fi generation carries two pairs of characters and is known as a dihybrid. When 

 dihybrids are bred, the F2 generation segregate in the ratio of 9, 3, 3, 1. 



WH. FITZ. AD. BIO. — 22 



