During prophase I of meiosis, the correct event that occurs is c) synapsis and crossing over. This stage is marked by the pairing of homologous chromosomes, a process known as synapsis. Each pair of homologous chromosomes aligns closely along their lengths, allowing for the exchange of genetic material between chromatids in a process called crossing over. This not only helps in increasing genetic variation but also plays a crucial role in ensuring proper segregation of chromosomes during the subsequent stages of meiosis.
In contrast, the other options relate to different stages or mechanisms that do not specifically occur during prophase I:
- a) Reduction in chromosome number occurs during anaphase I when the homologous chromosomes are separated.
- b) Segregation of alleles of unlinked genes refers to independent assortment, which occurs later in meiosis, not specifically during prophase I.
- d) Duplication of chromatids occurs prior to meiosis during the S phase of the cell cycle.
- e) Segregation of alleles of linked genes can happen during the process of crossing over, but the actual segregation occurs in the later phases of meiosis.
Thus, the defining characteristic of prophase I of meiosis is the pairing of homologous chromosomes followed by crossing over, making option c the right choice.