functions.php

<?php

/**
 * Add Site Description to Title 
 *
 */
function be_desc_in_title( $title, $inside, $wrap ) {

	$inside = '<a href="' . home_url() . '">' . get_bloginfo( 'name' ) . ' <span class="desc">' . get_bloginfo( 'description' ) . '</span></a>';
	
	//* Build the title
	$title  = genesis_html5() ? sprintf( "<{$wrap} %s>", genesis_attr( 'site-title' ) ) : sprintf( '<%s id="title">%s</%s>', $wrap, $inside, $wrap );
	$title .= genesis_html5() ? "{$inside}</{$wrap}>" : '';
	return $title;	
}
add_filter( 'genesis_seo_title', 'be_desc_in_title', 10, 3 );