Question

Explain two phenomena which lead to variation in DNA.

Hint:

One phenomenon changes the DNA letters themselves; the other reshuffles existing alleles.

Answer 1

Step 1: Understanding the Concept:
DNA is copied with very high accuracy at each cell division, but it is not copied perfectly. The small errors and rearrangements that do occur are what create variation between individuals.

Step 2: Explain mutation.
A mutation is a permanent change in the DNA base sequence, for example a base being wrongly copied, added, or deleted during replication, or damage from radiation or chemicals. This directly changes the genetic information at that spot, sometimes changing the protein it codes for.

Step 3: Explain recombination.
During meiosis, homologous chromosomes pair up and can exchange corresponding segments in a process called crossing over. This shuffles existing alleles into new combinations on the same chromosome, without changing the DNA sequence of any single gene.

Final Answer:
Mutation (a direct change in DNA sequence) and recombination (crossing over during meiosis) are the two main phenomena that create DNA variation.