The correct answer is option B, Anaphase I.

Explanation:
Mendelian factors or genes segregate during the process of meiosis. Meiosis is a type of cell division that occurs in the reproductive cells of sexually reproducing organisms. During meiosis, the chromosome number is reduced by half, from diploid (2n) to haploid (n).

The segregation of Mendelian factors occurs during the first division of meiosis, which is called meiosis I. Meiosis I consists of four stages: prophase I, metaphase I, anaphase I, and telophase I.

During prophase I, the homologous chromosomes pair up and exchange segments of DNA through a process called crossing over. This results in the formation of new combinations of genes on the chromosomes.

During metaphase I, the homologous chromosomes line up at the equator of the cell.

During anaphase I, the homologous chromosomes separate and move towards opposite poles of the cell. This is the stage where the segregation of Mendelian factors occurs. Each chromosome contains two copies of each gene, one from each parent. During anaphase I, the homologous chromosomes separate and each daughter cell receives only one copy of each gene.

During telophase I, the chromosomes reach the opposite poles of the cell and the cell divides into two daughter cells. Each daughter cell contains half the number of chromosomes as the original cell.

In conclusion, the segregation of Mendelian factors occurs during anaphase I of meiosis.