Question

All of the following are sexual sources of genetic variation except

• A. Random fertilization
• B. Mutation
• C. Crossing-over
• D. Production of offspring from two parents

Answer 1

The correct option is B

Mutation

The correct option is B

Explanation of the correct option :

1. Mutation is the change in the nucleotides of DNA.
2. This results in the change of the gene sequence of that organism.
3. Mutation can naturally occur during the DNA replication process before cell division.
4. Apart from this,DNA mutations can also be induced by exposure to UV rays, viral infections, food colouring agents etc.
5. As a result of mutation, variation occurs in the genetic material of an organism.
6. But mutations can never be a sexual source of genetic variation.
7. As mutations cannot occur during sexual events like fertilization.

Explanation of the incorrect option:

Option A:

1. Random fertilization means the chance of fusion of any one sperm with an ovum during sexual reproduction when millions of sperms are produced.
2. As here, there is fusion of male and female gametes, so it will result in genetic variation.

Option C:

1. Crossing-over is the event where there is exchange of DNA segments between two non-sister chromatids of a homologous pair of chromosome during meiosis (occurs during gamete formation in sexual reproduction).
2. As here, DNA segments are exchanged so it will lead to genetic variation.

Option D:

1. Production of offspring from two parents means sexual reproduction.
2. So there will be crossing over during gamete formation as well as fusion of two different gametes, resulting in genetic variation.

Final answer: All of the following are sexual sources of genetic variation except mutation.