10 AN INTRODUCTION TO MODERN GENETICS 



CHAPTER PAGE 



C. THE THEORY OF POLYPLOIDS 



1. The appearance of polyploids 67 



2. Meiotic behaviour and segregation in polyploids 



(a) Autopolyploids 68 



(b) Allopolyploids 71 



3. Auto- and allo-syndesis 73 



4. Secondary pairing 73 



III. The Behaviour of Individual Chromosomes 75 



A. SEX CHROMOSOMES 



1. Types of sex chromosomes 75 



2. Cytological behaviour of the sex chromosomes 76 



3. Sex chromosomes in polyploids 79 



4. Sex-linked inheritance 79 



B. NON-DISJUNCTION 



1. Non-disjunction of X 81 



2. Non- disjunction of other chromosomes in Drosophila 82 



3. Non-disjunction in other organisms 83 



4. Segregation in trisomies: secondary non-disjunction 84 



5. Chromosome mosaics 84 



IV. The Linear Differentiation of the 



Chromosomes 89 



A. CROSSING-OVER 



1 . Cross-over maps 89 



2. Maps prepared on other bases 92 



3. Genetic and environmental effects on crossing-over 92 



4. The physical reality of the cross-over map 94 



5. Salivary gland chromosomes 98 



6. "Lampbrush" Chromosomes. loi 



7. Genetic analysis of the process of crossing-over loi 



8. Crossing-over in polyploids 105 



B. TRANSLOCATION 



I. Datura secondaries and tertiaries 108 



2 Segmental interchange 109 



