Can you suggest an adaptive value for reatining the tetrad formation?
A tetrad is what is formed when homologous chromosomes pair up and synapse during prophase I of meiosis. Since each chromosome at that point consists of 2 sister chromatids joined together at their centromere, when two homologous chromosomes synapse the result has a total of four chromatids (tetra = 4, hence, tetrad). In a tetrad, crossing over occurs, which is the exchanging of corresponding segments of non-sister chromatids of homologous chromosomes. In simpler terms, a single crossing over event might take a segment from maternal chromosome 3 and swap it with the same segment of the paternal chromosome 3, resulting in 2 chromosomes that have both maternal and paternal segments. This exchange of chromosomal segments shuffles the genetic information, creating new combinations of alleles, and so creates greater variety among the gametes. This in turn produces greater genetic variation among individuals, which is advantageous for evolution.
