AP BIOLOGY

Detailed explanation-1: -The cells begin to divide, and the chromosomes pair up, forming a structure called a tetrad, which contains four chromatids. As homologous chromosomes pair up and form tetrads, they undergo a process called crossing-over.

Detailed explanation-2: -Homologous chromosomes containing the two chromatids come together to form tetrads, joining at their centromeres (2n 4c). This is when “crossing over” occurs, which creates genetic variation.

Detailed explanation-3: -During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. Chromosomal condensation allows these to be viewed in the microscope.

Detailed explanation-4: -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.

Detailed explanation-5: -Tetrad formation occurs during pachytene stage wherein the process of crossing over takes place. During this stage, the non-sister chromatids of homologous chromosomes may exchange segments over regions of homology. At the sites where the exchange takes place, the chiasmata is formed.