Ultra-violet light causes

Options

A. Formation of pyrimidines dimers
B. Sticky metaphases
C. Photodynamic action
D. Destruction of hydrogen bonds between complementary DNA strands.

Answer

**Step-by-Step Solution:**

1. **Understanding Ultraviolet Light:**
- Ultraviolet (UV) light is a type of high-energy radiation that can have harmful effects on living organisms, particularly on DNA.

2. **Role of the Ozone Layer:**
- The ozone layer in the stratosphere absorbs a significant amount of UV radiation, protecting life on Earth from its harmful effects. However, depletion of the ozone layer has led to increased exposure to UV light.

3. **Effects of UV Light on DNA:**
- UV light can cause damage to the DNA structure. One of the most significant types of damage is the formation of pyrimidine dimers.

4. **Formation of Pyrimidine Dimers:**
- Pyrimidine dimers occur when adjacent pyrimidine bases (such as thymine) bond with each other instead of bonding with purine bases (adenine or guanine). This abnormal bonding distorts the DNA structure.

5. **Consequences of Pyrimidine Dimer Formation:**
- The distortion in DNA structure can lead to mutations. These mutations can result in various health issues, including skin cancers and other diseases.

6. **Evaluating the Options:**
- The question presents several options regarding the effects of UV light:
- Formation of pyrimidine dimers (correct)
- Sticky metaphases (incorrect)
- Photodynamic action (incorrect)
- Destruction of hydrogen bonds between complementary DNA strands (incorrect)

7. **Conclusion:**
- The correct answer to the question "Ultraviolet light causes" is the formation of pyrimidine dimers.

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