Biotechnology

The first recombinant DNA (r-DNA) was constructed in the bacterium Escherichia coli (E. coli)} in 1972 by Paul Berg.
It was a significant step in genetic engineering and molecular biology.

Transgenic animals are those that have had a foreign gene deliberately inserted into their genome.
Transgenic mice are widely used for testing the safety of vaccines, including the polio vaccine.
These mice help assess the toxicity and immunogenicity of a vaccine before it's used in humans.
Other animals like sheep and goats may be used for producing recombinant proteins, but not for vaccine safety testing.

Restriction endonucleases are enzymes that cut DNA at specific recognition sites.
Hind II was the first restriction enzyme discovered that cuts DNA at a specific recognition sequence.
It recognizes a sequence of exactly six base pairs and cuts DNA at that site.
Hence, the correct answer is six base pairs.

Step 1: Transgenic microorganisms are genetically engineered to express foreign genes.
Step 2: These microbes act as miniature factories that produce proteins such as insulin, growth hormone, etc.
Step 3: Both assertion and reason are true and closely linked—reason supports assertion directly.

Step 1: Bacillus thuringiensis} produces a crystalline protein toxin called Bt toxin.
Step 2: The toxin is produced in an inactive form called protoxin.
Step 3: It becomes active only in the alkaline pH of the insect gut.
Step 4: Since the bacteria’s own cytoplasm doesn't activate the toxin, it is not harmed.

Step 1: Ori (origin of replication) is a DNA sequence where replication starts.
Step 2: In genetic engineering, Ori determines how many copies of the inserted DNA will be made inside the host cell.
Step 3: Selectable marker identifies transformed cells, not replication.