What mechanisms prevent interspecies and same-sex breeding?

The cell biology of mammalian fertilization. (a) Diagram highlighting the main cellular features of both the mammalian sperm and egg important during fertilization. (b) Schematics showing the four main steps in mammalian fertilization. (1) Sperm undergo the acrosome reaction and pass through the egg investments: the cumulus cells and the zona pellucida. (2) The acrosome reaction triggers the re-localization of Izumo1 (red) from the acrosomal membrane to the sperm head plasma membrane. (3) Once within the perivitelline space, the now exposed Izumo1 ligand is able to interact with the egg receptor Juno (green) displayed on the oolemma. (4) Finally, the sperm and egg membranes fuse, fertilizing the egg.

(a) perivilelline zunu pcllucldu(ZP) spam: (va) ”V Wk” 1. acrosome reaction 2. ZP penetration cumulus cells E i i L 3. spemregg binding 4. fusion 001mm!”