Question

The ultimate source of variations is

• A. natural selection
• B. sexual reproduction
• C. mutations
• D. hormonal actions

Answer 1

The correct option is (B):

Explanation of the correct option:

1. The ultimate source of all variations is mutation.
   
2. Mutation changes the genetic makeup (genes) of an organism which can alter the functions.
   
3. It occurs due to sudden change caused by a chemical agent or physical agents called the mutagen.
   
4. It is called the ultimate source of variation as it causes the change at genetic level of the organism.

Explanation of the incorrect options:

Option (A):

1. Natural selection is an important mechanism of evolution.
2. It states that the organisms that are able to survive and reproduce with the changing environmental conditions are selected by nature while the ones that cannot survive are eliminated.
3. The genes responsible for the survival of an organism are passed on to the successive generations.
4. But the changes in genes is caused by mutation, hence, mutation ultimately leads to natural selection.

Option (C):

1. Sexual reproduction is a process where two parents participate in producing their offspring.
2. The following events may occur during sexual reproduction:
3. Error in copying of DNA, which are not highly significant.
4. Random segregation of paternal and maternal chromosome at the time of gamete formation.
5. Exchange of genetic material between homologous chromosomes during the formation of gametes.
6. Again, all these changes cause the change in genes and any alteration in in genes is mutation.

Option (D):

1. ​Hormonal actions are not responsible for causing variations in the genetic character.
   
2. It can only alter the functioning of specific target organs.
   
3. These changes are not inheritable.

Final Answer: The ultimate source of variations is mutations.