Answer:
By the process of extraction of better DNA and then combining that with another DNA.
Explanation:
There are many definitions of genetic engineering, but in short, from all definition, it can be said that genetic engineering is the extraction of DNA of any organism's genome and then combine it with the genome of another organism.
Now let's come, how it helps in agriculture.
Suppose you have a rice variety named A, which gives less yield or harvested food. Along with this, it has long leaves, which you don't like. You heard about another rice variety named B, which has short leaves and gives more yields or harvested food than your ones. Now you want to get the character of variety B in your variety A. Genetic engineering will help you to do this. How? Please read below:
Scientists at first take that part of DNA from variety B, which is responsible for short leaves and more yield. Then they cut that using restriction enzyme. After that, they will combine it with the DNA of variety A. Before combining, they will remove the gene which is responsible for long leaves and less yield. For combining the DNA of B variety, they will use the DNA ligase enzyme.
After that, they will keep it in-vitro condition means under a controlled environment so that the new variety named C can produce. After producing variety C, they will test its compatibility with soil in their experimental field. If the result is positive, then they make a test on the different types of soil. If the result is positive for all soils, they will release it as a new variety.
This is applicable to livestock too. Scientists cut the DNA using the restriction enzyme and then combine it using the ligase enzyme. Then they produced an improved one.
Genetic engineering helps in this way in agriculture to increase the amount of harvested food
