AP BIOLOGY

Detailed explanation-1: -After complete cell division, each chromosome contains two sister chromatids .

Detailed explanation-2: -During prophase I and metaphase I of meiosis, a chromosome consists of a tetrad (4 chromatids or 4 DNA molecules) and is reduced to two chromatids (2 DNA molecules) by the time metaphase II occurs.

Detailed explanation-3: -At meiosis, each of the homologous chromosomes is comprised of two identical chromatids joined together by a common kinetochore (centromere). The identical chromatids are specifically called sister chromatids to distinguish them from the so-called non-sister chromatids.

Detailed explanation-4: -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. Note that the bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.

Detailed explanation-5: -Each pair of chromosomes-called a tetrad, or a bivalent-consists of four chromatids. At this point, the homologous chromosomes exchange genetic material by the process of crossing over (see linkage group).