Table 2.

Number of Z chromosome combinations in Los Angeles (UCLA) and New York (Rockefeller University) colonies

Sex	Z chr (a)	Z chr (b)	Birds
Male	Zsm	Zm	8
Male	Zsm	Zsm	11
Male	Zm	Zm	3
Female	Zsm		7
Female	Zm		1

The type of Z chromosome polymorphism was checked by karyotyping and PCR. Although PCR could predict karyotype in a majority of samples, two samples in Zsm/Zsm male group showed a mismatch of the Z chromosome karyotype and the PCR result. Since these two males were from same parents (New York colony), it is possible that there is a population which does not have correlation of Z chromosome type and existence of insertion