Disjunction refers to

Options

A. the separation of homologous chromosomes at anaphase I
B. the type of chromosomal aberration in which there is loss of a part of a chromosome
C. incopatibility in fungi and other thallophytes
D. modification of gene action by a nonallelic gene.

Explanation

**Step-by-Step Solution:**

1. **Understanding Disjunction**: Disjunction is a biological term that refers to the separation of chromosomes during cell division.

2. **Context in Cell Division**: Disjunction specifically occurs during meiosis, which is the type of cell division that produces gametes (sperm and eggs).

3. **Identifying the Phase**: In meiosis, disjunction occurs during Anaphase I. This is the stage where homologous chromosomes, which are pairs of chromosomes containing the same genes but possibly different alleles, are separated.

4. **Process of Disjunction**: During Anaphase I, the homologous chromosomes are pulled apart to opposite poles of the cell. This separation is crucial for ensuring that each gamete receives only one chromosome from each pair.

5. **Conclusion**: Therefore, disjunction refers to the separation of homologous chromosomes at Anaphase I of meiosis.

**Final Answer**: Disjunction refers to the separation of homologous chromosomes at Anaphase I of meiosis.

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