Males have more Z chromosome-linked HSD17B4 DNA. (A) Southern blot hybridization of HaeIII and HindIII digested genomic DNA from male (M) and female (F) of zebra finch probed with 32P-labeled zebra finch HSD17B4 EST CK313884. In both digest samples, the blot showed bands of stronger signal in males than females, suggesting Z chromosome linkage of HSD17B4. (B) Z chromosome localization of HSD17B4 sequence confirmed by FISH analysis. Individual fluorescently stained chromosomes are in the background, and two distinct, sharp hybridization signals over the Z chromosome show label on the two copies of the HSD17B4 gene (arrowhead). The Z-linked 094L04 BAC probe encoding HSD17B4 also cross-hybridized to the W chromosome, suggesting that it contains repetitive sequences such as ZBM that are present on both Z and W . Scale bar = 10 μm.