RNA expression; effects of the mutation on Hr mRNA levels. Total RNA was extracted from dorsal skin of each genotype at different ages (1, 7, 14, 35 days after birth). A probe designed to span exon 12 of the Hr cDNA was amplified from wild-type skin cDNA using polymerase chain reaction. From the left side, lanes and samples are as follows: lane 1, 1 day, +/+; lane 2, 1 day, Hrrh-R/+; lane 3, 1 day, Hrrh-R/Hrrh-R; lane 4, 7 days, Hrrh-R/+; lane 5, 7 days, Hrrh-R/Hrrh-R; lane 6, 14 days, +/+; lane 7, 14 days, Hrrh-R/+; lane 8, 14 days, Hrrh-R/Hrrh-R; lane 9, 35 days, Hrrh-R/+; lane 10, 35 days, Hrrh-R/Hrrh-R. Arrow indicates the position of Hr transcript. The bottom panel represents the intensity of 28S rRNA from the ethidium bromide–stained gel as a loading control.