AP BIOLOGY

Detailed explanation-1: -Meiosis I. Meiosis I segregates homologous chromosomes, which are joined as tetrads (2n, 4c), producing two haploid cells (n chromosomes, 23 in humans) which each contain chromatid pairs (1n, 2c). Because the ploidy is reduced from diploid to haploid, meiosis I is referred to as a reductional division.

Detailed explanation-2: -Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination.

Detailed explanation-3: -During zygotene, homologous chromosomes form tetrads by the process of synapsis (pairing of homologous chromosomes). Formation of synaptonemal complex is also seen during this stage. Q. Tetrad formation occurs in phase of prophase I of meiosis I.

Detailed explanation-4: -Tetrads only form in meiosis I for the purpose of crossing over. In meiosis II, the number of chromosomes has already been reduced, so homologous pairs are not present to form tetrads.

Detailed explanation-5: -Tetrad formation occurs during the zygotene stage of meiotic prophase. It is a meiotic-specific process. Homologous chromosomes are DNA fragments within a diploid organism of the same size one from each parental source.