Chapter I: Part I: Introductory 5

Mendel's law of segregation 5
Linkage and chromosomes 5

Crossing-over 7

The Y chromosome and non-disjunction 8

Mutation in _Drosophila ampelophila_ 10
Multiple allelomorphs 11
Sex-linked lethals and the sex ratio 14
Influence of the environment on the realization of two
sex-linked characters 16
Sexual polymorphism 17
Fertility and sterility in the mutants 18
Balanced inviability 19
How the factors are located in the chromosomes 20
The sex-linked factors of _Drosophila_ 21
Map of chromosome X 22
Nomenclature 24