With reference to the latest developments in stem cell research, consider the following statements: 1. The only source of human stem cells are the embryos at blastocyst stage 2. The stem cells can be derived a without causing destruction to blastocysts 3. The stem cells can regenerate themselves in vitro virtually forever 4. Indian research centres also created a few cell lines which can be developed into many types of tissues Which of these statements are correct?

1. Statement 1 is incorrect. While embryos at the blastocyst stage are a primary source, human stem cells can also be obtained from other sources like umbilical cord blood and adult tissues (though adult stem cells have limitations compared to embryonic ones). 2. Statement 2 is incorrect. Historically, deriving embryonic stem cells involved the destruction of the blastocyst. While research explores alternatives, this was the standard method. 3. Statement 3 is correct. Embryonic stem cells possess the characteristic of self-renewal, allowing them to regenerate themselves in vitro (in a lab setting) for extended periods, potentially virtually forever under appropriate conditions. 4. Statement 4 is correct. Several Indian research centres have been actively involved in stem cell research and have successfully established cell lines capable of differentiating into various types of tissues. 5. Therefore, only statements 3 and 4 are correct.