The randomness in the alignment of recombined chromosomes at the metaphase plate, coupled with the crossing over events between nonsister chromatids, are responsible for much of the genetic variation in the offspring. To clarify this further, remember that the homologous chromosomes of a sexually reproducing organism are originally inherited as two separate sets, one from each parent. Using humans as an example, one set of 23 chromosomes is present in the egg donated by the mother. The father provides the other set of 23 chromosomes in the sperm that fertilizes the egg. Every cell of the multicellular offspring has copies of the original two sets of homologous chromosomes. In prophase I of meiosis, the homologous chromosomes form the tetrads. In metaphase I, these pairs line up at the midway point between the two poles of the cell to form the metaphase plate. Because there is an equal chance that a microtubule fiber will encounter a maternally or paternally inherited chromosome, the arrangement of the tetrads at the metaphase plate is random. Thus, any maternally inherited chromosome may face either pole. Likewise, any paternally inherited chromosome may also face either pole. The orientation of each tetrad is independent of the orientation of the other 22 tetrads.
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The bacterial flora in the intestines are essential to homeostasis in the body, they not only break down food so the nutrients can be absorbed, they produce vitamins like biotin and vitamin K and guard against harmful bacteria that enter the system. While your heart is a vital organ, the brain (and the nervous system that attaches to the brain) make up the most critical organ system in the human body. The digestive system ordinarily gets 20% to 25% of the oxygenated blood pumped out by the heart and the receptors in muscles provide the brain with information about body position and movement, the brain controls the contraction of skeletal muscle the nervous system regulates the speed at which food moves through the digestive tract.
