a, Temporal dynamics of meiotic genes during ovary development. SYCP1 is not expressed in human ovary. The genes SPO11 and STAG3 are not present in the chicken gene annotations used in this work. b, Expression of STRA8 during ovary development. The vertical bars show the range between the replicates and the horizontal dashed line marks 1 RPKM. c, Temporal dynamics of meiotic genes during testis development. The profiles of STRA8 and DMC1 are represented not by their range of expression but by their highest peak of expression. In rhesus macaque, meiosis is known to start around 3–4 years36; our data suggest it had not yet started in the 3-year-old individuals examined. STRA8 is lowly expressed in the human testis. d, Expression of STRA8 during testis development. The vertical bars show the range between the replicates and the horizontal dashed line marks 1 RPKM. e, PCA of ovary and testis development for each species (n = 21,798 protein-coding genes in mouse, 19,390 in rat, 19,271 in rabbit, 20,345 in human, 21,886 in rhesus macaque, 21,304 in opossum and 15,481 in chicken).