Because gametes (sex cells) are the only cells that pass along genetic information. Somatic cells are the cells that have already differentiated into various organs or tissues. They can't pass on a mutation to offspring because they're not involved in creating it.
The answer is D. They fuse during sexual reproduction
This either attaches the virus to the host cell or dissolves the membrane letting the virus into the host cell. The viral enzymes(enzymes are again chemical compounds) multiply the viral dna copies and viral protiens. These are new viruses. These new viruses breakout of the cell to infect other cells.
Populations evolve and individual organisms do not. Evolution occurs through natural selection and survival of the fittest as populations evolve traits that better suit their environment.
That this is the desired response at this stage of gestation
