PROBLEM 5. Breeding Neiv Types 



have been established. You already know 

 rli;it hornlessness is a dominant mutation. 



Before fox farming was begun early in 

 this century a mutation from the com- 

 mon red fox to the so-called black or sil- 

 ver fox had apparently occurred twice. 

 One seems to have occurred in eastern 

 Canada, the other in Alaska. These muta- 

 tions have proved to be of considerable 

 economic importance since silver foxes 

 are now raised in large numbers. 



The plant breeder has a better chance 

 of findiuCT p-ene or chromosomal changes 

 than the animal breeder. Plants, as a rule, 

 have so many more offspring that there 

 is a greater chance that changes will oc- 

 cur. There are many examples of such 

 changes. Figure 446 shows you the result 

 of one very profitable chromosomal 

 change. Many years ago in Brazil a seed- 

 less orange appeared on an ordinary 

 orange tree. Naturally, this particular 

 mutation could become established only 

 through vegetative propagation. A wild 

 common yellow sunflower in Boulder, 

 Colorado, suddenly produced a red blos- 

 som. In 1895 a florist near Boston dis- 

 covered a mutation among ferns which 

 had grown wild, unchanged, for a cen- 

 tury. This became the desirable Boston 

 fern used so much as a house plant. 

 Within a few years there appeared in 

 five different states six mutations of nor- 

 mal Boston ferns. By 1947 m«re than 

 two hundred varieties had come into ex- 

 istence. 



These are but a few examples of gene 

 and chromosomal chano-es that have oc- 

 curred; some are useful to the breeder, 

 some are of little or no commercial im- 

 portance. In such cases the breeder lets 

 the new form die out. 



of An'mmls and Plants 



499 



Fig. 449 At the left is one leaf from a Boston 

 fern. The other leaves are a few of the more 

 than two hundred varieties of the Boston fern 

 that have come into existence by mutation. 

 All these mutations have occurred smce /A'pj'. 



(BROOKLYN BOTANIC GARDEN) 



The third method — uniting desirable 

 characters in one variety. This third 

 method used by breeders has great pos- 

 sibilities. The method is based on cross- 

 breeding. Some cattle in our southern 

 states produce good meat but they are 

 unable to endure intense heat and they 

 are susceptible to the disease known as 

 Texas fever. Brahman cattle, a breed 

 originally imported from India, thrive 

 in a hot climate and are resistant to 

 Texas fever but the quality of their 

 meat is poor. For some fifteen years ex- 

 periments were carried on in crossmg 

 Brahman cattle wuth our native good beef 

 cattle. This cross breeding, or hybridi- 

 zatio?7, resulted in the Brahman-Short- 

 horn breed which combines in one or- 

 ganism the good qualities of both the 



