THE DAZ GENE-CLUSTER ON THE HUMAN Y-CHROMOSOME AROSE FROM AN AUTOSOMAL GENE THAT WAS TRANSPOSED, REPEATEDLY AMPLIFIED AND PRUNED

It is widely believed that most or all Y-chromosomal genes were once s hared with the X chromosome. The DAZ gene is a candidate for the human Y-chromosomal Azoospermia Factor (AZF). We report multiple copies of DAZ (>99% identical in DNA sequence) clustered in the AZF region and a functional DAZ homologue (DAZH) on human chromosome 3. The entire gen e family appears to be expressed in germ cells. Sequence analysis indi cates that the Y-chromosomal DAZ cluster arose during primate evolutio n by (i) transposing the autosomal gene to the Y, (ii) amplifying and pruning exons within the transposed gene and (iii) amplifying the modi fied gene. These results challenge prevailing views of sex chromosome evolution, suggesting that acquisition of autosomal fertility genes is an important process in Y chromosome evolution.