Final answer:
In biology, the ureteric bud bifurcates and joins with the metanephric blastema during embryonic development, which is crucial for the formation of the urinary system.
Step-by-step explanation:
The question 'UB bifurcates and joins at ______.' is related to biology, particularly human anatomy. UB typically refers to the ureteric bud, a structure involved in the development of the urinary system, specifically the ureters, renal pelvis, calyces, and, in some species, a portion of the kidney. During embryonic development, the ureteric bud arises from the mesonephric duct (Wolffian duct) and eventually bifurcates and joins with the metanephric blastema to give rise to the aforementioned structures. Understanding this process is crucial in comprehending how the urinary and renal systems develop.