3i8 



ELEMENTS OF BIOLOGY 



of the egg become synaptic mates and the chromosome complex, 

 containing two X members, is that of the female of the species. If 

 the fertilizing sperm is one which contains the PY chromosome, 

 then the new animal has the chromosomal makeup of the male. 



We may now think of p and m, and of P and P\ and M and M\ 

 as representing paternal and maternal chromosomes. To analyze, P 



SPERMS 



MALE 



OVUM 



FEMALE 



Fig. 203. — Diagrams of fertilization and the formation of the diploid number of 

 chromosomes in the dividing egg. Note that two possibilities as regards the X 

 chromosomes are shown. Compare with Fig. 201 and Fig. 202. 



in the new generation contains chromatin from both p and m of the 

 male parental nucleus, and M contains elements from both p and m 

 of the mother. To go back another generation, p of the male parent 

 and in of the male parent both contained p and m elements from 

 his parents; similarly, in previous maternal generations, p and m 

 members of synaptic pairs were derived from synaptic pairs of previ- 

 ous generations. Thus there is a continuity of chromatin material 



