Class 12-science

first see your interest than take decision its all depends on you.all the best

As per CBSE student cannot change its stream in class 12 and also in mid stream of class 11. And you might also face problem from changing your stream from comm without maths to science with maths. The link for the same is given below:
http://m.indiatoday.in/education/story/cbse-would-not-permit-stream-change-in-class-11/1/440132.html

If you have taken not maths with PCB then you may not able to do Engineering. However to full fill your dream, you can take BCA-MCA route to be a software engineer. You may do courses and certifications to top up your hardware knowledge and skills .

You can do BSc Genetics. This course is offered by very limited colleges in India. You can do BSc is Botany and then specialize in Genetics at postgraduate level.

Dear Bodakunta ,
You can do your personal development with the right education and knowledge. What ever experience you would face in coming year take it in positive way and learn from your mistake.
Now about your career there is lots of option available in the education world.If you can provide me your career aim and short introduction than i would assist you to find the best course .
All the best

Hi Mohit
Merchant navy can be joined after 10th as seafarer after qualifying pre sea courses or after 12th as an officer through various degree or diploma courses in mainly two specialized fields, Nautical (Deck) and Marine engineering so if you hv no financial burden, complete your 12th with PCM and then go for officer's training directly.

Dear student, it depends on your concentration and sitting capacity. if you feel that you can study 5-8 hours daily in home with full concentration then you can go for self-study as it the best way to qualify exams only if your concepts are clear in advance. if you want to memorize the things in routine with an assessment basis, then move to some good coaching institution nearby. you can make use of mock-test programs in parallel with self study, if suits you. all the best.