Genetics And Evolution

Step 1: Understand the meaning of a zygote.
A zygote is a eukaryotic cell formed by the fertilization of an egg and a sperm cell. It's a single-cell embryo that will eventually develop into a multicellular organism.
Step 2: Know the methods used to introduce DNA into a zygote.
Microinjection: A fine glass needle is used to directly inject DNA into the zygote. This is a common and precise method used in genetic engineering of animals.
Electroporation: High-voltage electrical pulses create pores in the cell membrane of the zygote, allowing DNA to enter. It is effective in making cells temporarily permeable.
Transduction: Involves the use of viruses to deliver foreign DNA into a host cell. Modified viruses can be used to introduce DNA into eukaryotic zygotes.
Step 3: Understand why conjugation is not applicable.
Conjugation is a natural gene transfer process seen in prokaryotes (like bacteria), where DNA is transferred through a pilus between two bacterial cells.
It is not used and not possible for transferring DNA into a eukaryotic zygote because conjugation mechanisms do not exist in eukaryotic systems. Step 4: Conclude based on the above facts.
All the first three techniques (Microinjection, Electroporation, Transduction) are artificial and suitable for zygotes. Conjugation is strictly bacterial and irrelevant to genetic manipulation of zygotes.

Step 1: Understanding Bt CryA protein.
Bacillus thuringiensis (Bt) produces Cry proteins, which are used in genetically modified crops to provide pest resistance.
Step 2: Activation of CryA protein.
When caterpillar pests ingest CryA protein, it reaches their gut, where the alkaline pH environment activates the CryA protein. This activated toxin binds to the gut epithelial cells of the insect, leading to cell lysis and ultimately killing the pest.
Step 3: Eliminate other options.
Option (1): CryA is not activated in acidic pH.
Option (3): CryA doesn't repel insects; it kills them.
Option (4): It does not induce satiation.
Thus, the correct answer is that CryA becomes toxic in the alkaline medium of the caterpillar gut.