The correct answer is option 1: a transgenic organism has a foreign gene inserted in its genome.

Option 1 states that a transgenic organism has a foreign gene inserted in its genome. This means that the organism has DNA from another species inserted into its own DNA. This foreign gene can come from a different plant, animal, or even a bacterium. The purpose of inserting this foreign gene is to introduce specific traits or characteristics into the organism. For example, a transgenic plant may have a gene from a bacteria that makes it resistant to certain pests or diseases.

Option 2, which states that a transgenic organism is a bacterial strain used for transferring genes, is not correct. While bacteria can be used in the process of gene transfer, the term "transgenic organism" refers to any living organism that has had a foreign gene inserted into its DNA, not just bacteria.

Option 3, which suggests that transgenic organisms are bacteria of extraterrestrial origin, is also not correct. Transgenic organisms are created through genetic engineering techniques in a lab and do not have any connection to extraterrestrial bacteria.

Therefore, the correct answer is option 1: a transgenic organism has a foreign gene inserted in its genome.