Heredity and sex . divide. Consequently there are formed two kinds ofspermatozoa — one containing X and the other Y(Fig. 23, E). In the body cells and early germ-tract of the femaleof lygseus (Fig. 24, A), there are twelve ordinarychromosomes and two sex chromosomes, X and reduction there are seven double chromosomes,the two Xs having united when the other chromosomes 46 HEREDITY AND SEX united (B). Two divisions take place {C, D), when thetwo polar bodies are formed, leaving seven chromosomesin the egg (E). Each egg contains as a result only oneX chromosome. Any egg of lygseus fertili
Heredity and sex . divide. Consequently there are formed two kinds ofspermatozoa — one containing X and the other Y(Fig. 23, E). In the body cells and early germ-tract of the femaleof lygseus (Fig. 24, A), there are twelve ordinarychromosomes and two sex chromosomes, X and reduction there are seven double chromosomes,the two Xs having united when the other chromosomes 46 HEREDITY AND SEX united (B). Two divisions take place {C, D), when thetwo polar bodies are formed, leaving seven chromosomesin the egg (E). Each egg contains as a result only oneX chromosome. Any egg of lygseus fertilized by a sperm carrying anX chromosome produces a female that contains two OncopettcLS o B. Fig. 25. :e^ Xs or XX. Any egg fertilized by a sperni containinga Y chromosome produces a male that contains oneX and one Y, or XY. Another insect, Oncopeltus fasciatus, represents athird type in which the chromosome groups in themale and in the female are numerically alike and alikeas to visible size relations. THE MECHANISM OF SEX-DETERMINATION 47 In the body cells of the male there are sixteen chro-mosomes (Fig. 25, A). After reduction there are ninechromosomes — seven in a ring and two in the middle(B). The seven are the fused pairs or double chro-mosomes; the two in the middle are the sex chromo-somes that have not fused.
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Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectsex, bookyear1913
