Both the X and Y chromosomes have multiple copies of genes that are important for sperm differentiation. One of these genes is called Sly, which is on the Y chromosome and regulates sex chromosome expression and sperm differentiation. A recent paper looks at two Sly-related genes on the X chromosome, called Slx and Slx-like1, and finds that they are important for proper sperm differentiation, and thus male fertility. Images show the head-tail connections in sperm from normal (top left, middle) and Slx/Slx-like1-deficient mice. The reduced motility of sperm in Slx/Slx-like1-deficient mice is like due to these abnormal head-tail connections, including partially detached tails (top right), incorrect alignment of the head and tail (bottom left), or abnormally-shaped tails (bottom middle, right).
Reference: Julie Cocquet, Peter J. I. Ellis, Yasuhiro Yamauchi, Jonathan M. Riel, Thomas P. S. Karacs, Áine Rattigan, Obah A. Ojarikre, Nabeel A. Affara, Monika A. Ward, and Paul S. Burgoyne. Authors’ Molecular Biology of the Cell paper can be found here.