Mendelian factor (Aa) is segregated during

The correct option is Anaphase I.

To understand why segregation of Mendelian factors (alleles) occurs during Anaphase I, let us break down the biological process step-by-step:
1. Mendelian Factors (Alleles): In a heterozygous individual with genotype Aa, the two different alleles (A and a) representing a gene locus are located on homologous chromosomes at the same position.
2. Homologous Chromosomes: One homologous chromosome carries the allele 'A' and the other carries the allele 'a'. During the S phase of interphase, these chromosomes duplicate, resulting in sister chromatids, but the maternal and paternal chromosomes remain paired as homologous pairs.
3. Meiosis I: During Meiosis I, the primary objective is to separate homologous chromosome pairs.
4. Anaphase I: In Anaphase I, the homologous chromosomes of each pair migrate to opposite poles of the cell. Since the allele 'A' is on one homologous chromosome and 'a' is on the other, the separation of these homologous chromosomes directly leads to the segregation of the alleles 'A' and 'a' into different daughter cells.
5. Meiosis II (Anaphase II): During Anaphase II, sister chromatids of individual chromosomes are separated. Since the homologous chromosomes containing the different alleles (A and a) have already segregated into separate cells during Anaphase I, Anaphase II merely separates identical sister chromatids (unless crossing over occurred, but the primary segregation of maternal and paternal homologous chromosomes happens in Meiosis I).

Therefore, the segregation of the Mendelian factor (Aa) takes place during Anaphase I of meiosis.