Hello aspirant,

See, there is no disadvantage if you study both Biology and Mathematics in 12th, but full of advantages. This is because if you study both Biology and Mathematics, then you can have a lot of options whether you want to pursue medical or engineering. You can prepare JEE Mains, JEE Advanced, NEET and any other common entrance exams for medical, agriculture, engineering etc. as well. Also, you have options even after completing 12th to study any course without falling into only one zone. So no need to be worried, it's upto you whether you want to take up both the subjects or simply end up taking only one subject.

Hope, it helps you.