i would like to know the details of how i could pursue marine biology ,and its scope in india
If you're planning to choose pure biology BSc degree, then you can choose general BSc in Biology and then choose masters in microbiology, biotechnology, genetics or any life science specialisation of your choice. Otherwise if you're pretty sure about your specialisation, then you can choose. Genetics is a sub branch of microbiology, biotechnology, so you can opt for masters in genetics as well after BSc or BE in Biotechnology, Microbiology, etc.
Marine Biology is the study of environment and life in sea. After 12th PCB, you can go for BSc in Marine Science and later MSc, MPhil and PHd in Marine Biology. You can work as a Scientist or Marine Biologist in Fisheries Institutes/Centres.
