THE GENERAL ASPECTS OF HEREDITY 15 



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That segregation of factors really takes place during 

 meiosis (the period during which chromosome reduc- 

 tion occurs) has been shown by the formation of two 

 types of pollen grain in certain hybrid rice plants. In 

 these Fi hybrids half the pollen grains contain starch 

 grains, like the pollen grains of one parent, while the 

 other half contain no starch. Fig. 4, from a section 

 of an anther treated 

 with iodine, shows 

 the two types of pol- 

 len grains scattered 

 in equal numbers 

 through the anther. 



Thus in an organ- 

 ism which is hetero- 

 zygous for one pair 

 of characters, say 

 short hair (domin- 

 ant) or long " An- 

 gora " hair (reces- 

 sive) in guinea-pigs, 

 the Fj hybrid ani- 

 mals will have short 

 hair, and all their 

 cells w^ill contain a 

 pair of chromosomes 

 which differ in that 

 one chromosome 

 contains the deter- 

 miner for short coat, 



while its mate contains the determiner for long 

 coat. When the germ cells of this guinea-pig are 

 formed, this pair of chromosomes, like the other 

 pairs, is separated, and half the eggs or sperms, 

 as the case may be, get the chromosome with 

 the determiner for short hair, while the other half 

 receive its mate containing the determiner for long 



Fig. 4. — Photomicrograph showing 

 Segregation of Pollen Types in a 

 Rice Hybrid. (After F. R. Parnell.) 



