Interference is

Options

A. decrease in frequency of crossing over because of heterochromatin
B. chiasma at one point disfavours formation of chiasma at second point
C. both correct
D. none of the above

Answer

**Step-by-Step Text Solution:**

1. **Understanding Interference**: Interference is a genetic phenomenon that occurs during the process of meiosis, specifically during the crossing over of homologous chromosomes.

2. **Crossing Over**: During meiosis, homologous chromosomes can exchange segments of genetic material in a process known as crossing over or recombination. This typically occurs at points called chiasmata.

3. **Chiasmata Formation**: When a crossover event occurs at one chiasma, it can affect the likelihood of another crossover event occurring nearby on the same chromosome.

4. **Interference Defined**: Interference refers to the phenomenon where the formation of a chiasma at one location on a chromosome reduces the probability of a chiasma forming at a nearby location. This means that if one crossover occurs, it inhibits the occurrence of another crossover in the vicinity.

5. **Not Decrease in Frequency**: It is important to note that interference does not imply a decrease in the overall frequency of crossing over. Instead, it specifically refers to the spatial relationship between chiasmata.

6. **Factors Affecting Crossing Over**: Other factors, such as the presence of heterochromatin or centromeres, can influence the rate of crossing over but are not classified as interference.

7. **Conclusion**: Therefore, interference is a specific phenomenon related to the spatial arrangement of chiasmata during meiosis, where one crossover event inhibits the occurrence of another nearby.