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.
Explanation:
It helps classify animals according to their needs.
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Multifidus
What is multifidus?
The transversospinal group of deep back muscles includes the semispinalis, rotatores, multifidus, and other short, triangular muscles. They are shorter than semispinalis but longer than rotatores, and they are the thickest muscles in the transversospinal group. On either side of the vertebral column, from the cervical to the lumbar spine, there is a multifidus. Cervical multifidus, thoracic multifidus, and lumbar multifidus are the three regional subgroups of the group.
The spinal column is extended by the multifidus muscles. They contribute to the lateral flexion of the spine as well as some rotation of the vertebral bodies away from the side of contraction.
Multifidus: a muscle in the fifth and deepest layer of the back that helps to erect and rotate the spine by filling in the groove on either side of the spinous processes of the vertebrae from the sacrum to the skull.
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Atomic Mass is determined by the number of protons plus the number of neutrons.
