BMPR1B and cyst: In the ovaries of fetuses and newborn lambs homozygous for the FecBB mutation in BMPR1B, the oocytes of the primordial follicles are larger and contain a greater volume of mitochondria, smooth endoplasmic reticulum and ribosomes, suggesting that the mutant form of BMPR1B has influenced the process of germline cyst breakdown and led to follicles better equipped for the initiation of follicular growth (Reader et al., 2012).