172 THE CHROMOSOMES 
ATTACHMENT OF SEX-CHROMOSOMES TO 
AUTOSOMES 
If one or more genes for sex are present in a 
chromosome, that chromosome would be designated 
as a sex chromosome, but in order that the mecha- 
nism give a differential result such chromosome 
must be present in duplex (XX or ZZ) in some in- 
dividuals and simplex (X or Z) in others. It is not 
necessary in the simplex individual that one whole 
chromosome be absent, but only that one should lack 
factors for sex, as in the case of Y-chromosome 
in one type, and supposedly the W-chromosome in 
the other. 
There is still another situation in regard to the 
chromosomes that carry the sex genes. In a few 
cases there is more than a suspicion that they are 
attached to other chromosomes, or what amounts 
to the same thing,that the region of the chromosomes 
bearing sex determining genes lies at one end of an 
ordinary chromosome. In such cases two of these 
chromosomes with attached portions are supposed 
to be present in the female (the XX type), but in 
the male only one chromosome of the pair has the 
attached portion. The thread worm, Ascaris, is a 
case in point. It has been observed by Boveri, 
Boring, Frolowa, Mulsow, Kautsch, and Geinitz 
that occasionally one or two small detached pieces 
of chromosomes are found constantly present in 
certain individuals—pieces that show a tendency 
in certain cells to become attached, or associated 
