AP BIOLOGY

Detailed explanation-1: -Chromosomes become visible during prophase. Chromatin is in its least condensed stage during the interphase stage. It begins its condensation during the prophase stage and is visible until the end of cell division.

Detailed explanation-2: -Prophase I can be divided into several stages, as follows. Leptotene begins with the already replicated chromosomes becoming visible as thin threads. The two sister chromatids are so closely aligned that they are not distinguishable.

Detailed explanation-3: -During prophase, the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses. The chromatin coils and becomes increasingly compact, resulting in the formation of visible chromosomes.

Detailed explanation-4: -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-5: -Meiosis I, the first meiotic division, begins with prophase I. During prophase I, the complex of DNA and protein known as chromatin condenses to form chromosomes. The pairs of replicated chromosomes are known as sister chromatids, and they remain joined at a central point called the centromere.