Meiosis-specific component of some cohesin complex required during the initial steps of prophase I in male meiosis. Probably required during early meiosis in males for separation of sister chromatids and homologous chromosomes. Replaces RAD21 in premeiotic S phase (during early stages of prophase I), while RAD21 reappears in later stages of prophase I. Involved in synaptonemal complex assembly, synapsis initiation and crossover recombination between homologous chromosomes during prophase I. Not required for meiosis in females in young mice, while it is required later as mice age. Component of some meiotic cohesin complex composed of the SMC1 (SMC1A or SMC1B) and SMC3 heterodimer attached via their hinge domain, RAD21L which link them, and STAG3. In meiotic chromosomes, localized along axial elements in early meiosis: detectable on the axial elements in leptotene, and stays on the axial/lateral elements until mid pachytene. It then disappears and is replaced with RAD21. Compared to REC8, has mutually exclusive loading sites on the chromosomes: REC8 and RAD21L form distinct cohesin-enriched domains along the axial elements. Specifically expressed in male and female gonads (at protein level). Male mice are sterile due to defects in chromosome synapsis at prophase I, leading to an arrest at a zygotene-like stage leading to total azoospermia. Females are fertile but develop an age-dependent sterility. Belongs to the rad21 family.